Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.51   12.652%   $265.3067   $265.31   $265.30   $265.30  
  Purchase #2 $192.45   11.538%   $214.6549   $214.65   $214.65   $214.70  
  Purchase #3 $127.76   13.781%   $145.3666   $145.37   $145.35   $145.40  
  Purchase #4 $201.61   12.511%   $226.8334   $226.83   $226.85   $226.80  
  Purchase #5 $234.43   3.816%   $243.3758   $243.38   $243.40   $243.40  
  Purchase #6 $205.75   10.610%   $227.5801   $227.58   $227.60   $227.60  
  Purchase #7 $192.33   4.718%   $201.4041   $201.40   $201.40   $201.40  
  7 purchase totals = $1,389.84       $1,524.5216   $1,524.52   $1,524.55   $1,524.60