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 $208.47   8.571%   $226.338   $226.34   $226.35   $226.30  
  Purchase #2 $123.52   13.349%   $140.0087   $140.01   $140.00   $140.00  
  Purchase #3 $64.43   4.361%   $67.2398   $67.24   $67.25   $67.20  
  Purchase #4 $64.70   3.573%   $67.0117   $67.01   $67.00   $67.00  
  Purchase #5 $235.55   8.375%   $255.2773   $255.28   $255.30   $255.30  
  Purchase #6 $78.91   10.121%   $86.8965   $86.90   $86.90   $86.90  
  Purchase #7 $93.55   13.749%   $106.4122   $106.41   $106.40   $106.40  
  7 purchase totals = $869.13       $949.1842   $949.19   $949.20   $949.10