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 $50.43   9.718%   $55.3308   $55.33   $55.35   $55.30  
  Purchase #2 $129.81   5.771%   $137.3013   $137.30   $137.30   $137.30  
  Purchase #3 $175.97   13.438%   $199.6168   $199.62   $199.60   $199.60  
  Purchase #4 $205.31   10.357%   $226.574   $226.57   $226.55   $226.60  
  Purchase #5 $232.93   8.542%   $252.8269   $252.83   $252.85   $252.80  
  Purchase #6 $86.88   11.451%   $96.8286   $96.83   $96.85   $96.80  
  Purchase #7 $68.92   11.201%   $76.6397   $76.64   $76.65   $76.60  
  7 purchase totals = $950.25       $1,045.1181   $1,045.12   $1,045.15   $1,045.00