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 $182.56   11.733%   $203.9798   $203.98   $204.00   $204.00  
  Purchase #2 $209.26   7.204%   $224.3351   $224.34   $224.35   $224.30  
  Purchase #3 $214.33   8.698%   $232.9724   $232.97   $232.95   $233.00  
  Purchase #4 $81.25   3.820%   $84.3538   $84.35   $84.35   $84.40  
  Purchase #5 $88.50   13.791%   $100.705   $100.71   $100.70   $100.70  
  Purchase #6 $222.53   5.221%   $234.1483   $234.15   $234.15   $234.10  
  Purchase #7 $196.25   3.387%   $202.897   $202.90   $202.90   $202.90  
  7 purchase totals = $1,194.68       $1,283.3914   $1,283.40   $1,283.40   $1,283.40