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 $183.45   11.531%   $204.6036   $204.60   $204.60   $204.60  
  Purchase #2 $68.92   9.184%   $75.2496   $75.25   $75.25   $75.20  
  Purchase #3 $69.80   7.689%   $75.1669   $75.17   $75.15   $75.20  
  Purchase #4 $242.46   5.604%   $256.0475   $256.05   $256.05   $256.00  
  Purchase #5 $41.50   11.567%   $46.3003   $46.30   $46.30   $46.30  
  Purchase #6 $151.30   12.214%   $169.7798   $169.78   $169.80   $169.80  
  Purchase #7 $156.30   8.145%   $169.0306   $169.03   $169.05   $169.00  
  7 purchase totals = $913.73       $996.1783   $996.18   $996.20   $996.10