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 $201.98   12.354%   $226.9326   $226.93   $226.95   $226.90  
  Purchase #2 $111.63   6.346%   $118.714   $118.71   $118.70   $118.70  
  Purchase #3 $52.77   7.495%   $56.7251   $56.73   $56.75   $56.70  
  Purchase #4 $240.26   13.729%   $273.2453   $273.25   $273.25   $273.20  
  Purchase #5 $50.72   11.105%   $56.3525   $56.35   $56.35   $56.40  
  Purchase #6 $182.97   12.518%   $205.8742   $205.87   $205.85   $205.90  
  Purchase #7 $222.60   10.809%   $246.6608   $246.66   $246.65   $246.70  
  7 purchase totals = $1,062.93       $1,184.5045   $1,184.50   $1,184.50   $1,184.50