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 $69.28   9.505%   $75.8651   $75.87   $75.85   $75.90  
  Purchase #2 $15.26   12.843%   $17.2198   $17.22   $17.20   $17.20  
  Purchase #3 $211.34   10.377%   $233.2708   $233.27   $233.25   $233.30  
  Purchase #4 $170.59   11.517%   $190.2369   $190.24   $190.25   $190.20  
  Purchase #5 $55.87   8.275%   $60.4932   $60.49   $60.50   $60.50  
  Purchase #6 $97.79   8.413%   $106.0171   $106.02   $106.00   $106.00  
  Purchase #7 $104.67   4.140%   $109.0033   $109.00   $109.00   $109.00  
  7 purchase totals = $724.80       $792.1062   $792.11   $792.05   $792.10