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 $56.76   10.184%   $62.5404   $62.54   $62.55   $62.50  
  Purchase #2 $229.35   6.807%   $244.9619   $244.96   $244.95   $245.00  
  Purchase #3 $55.73   5.792%   $58.9579   $58.96   $58.95   $59.00  
  Purchase #4 $136.51   10.293%   $150.561   $150.56   $150.55   $150.60  
  Purchase #5 $86.58   7.619%   $93.1765   $93.18   $93.20   $93.20  
  Purchase #6 $155.28   8.417%   $168.3499   $168.35   $168.35   $168.30  
  Purchase #7 $154.89   12.107%   $173.6425   $173.64   $173.65   $173.60  
  7 purchase totals = $875.10       $952.1901   $952.19   $952.20   $952.20