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 $190.25   8.170%   $205.7934   $205.79   $205.80   $205.80  
  Purchase #2 $35.76   13.534%   $40.5998   $40.60   $40.60   $40.60  
  Purchase #3 $229.25   7.726%   $246.9619   $246.96   $246.95   $247.00  
  Purchase #4 $58.89   9.549%   $64.5134   $64.51   $64.50   $64.50  
  Purchase #5 $70.97   7.125%   $76.0266   $76.03   $76.05   $76.00  
  Purchase #6 $250.45   4.690%   $262.1961   $262.20   $262.20   $262.20  
  Purchase #7 $156.83   5.284%   $165.1169   $165.12   $165.10   $165.10  
  7 purchase totals = $992.40       $1,061.2081   $1,061.21   $1,061.20   $1,061.20