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 $87.93   9.756%   $96.5085   $96.51   $96.50   $96.50  
  Purchase #2 $104.85   5.815%   $110.947   $110.95   $110.95   $110.90  
  Purchase #3 $218.43   7.766%   $235.3933   $235.39   $235.40   $235.40  
  Purchase #4 $212.35   9.380%   $232.2684   $232.27   $232.25   $232.30  
  Purchase #5 $25.64   6.853%   $27.3971   $27.40   $27.40   $27.40  
  Purchase #6 $118.80   4.544%   $124.1983   $124.20   $124.20   $124.20  
  Purchase #7 $133.67   12.293%   $150.1021   $150.10   $150.10   $150.10  
  7 purchase totals = $901.67       $976.8147   $976.82   $976.80   $976.80