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 $148.56   13.267%   $168.2695   $168.27   $168.25   $168.30  
  Purchase #2 $97.84   6.520%   $104.2192   $104.22   $104.20   $104.20  
  Purchase #3 $9.39   5.244%   $9.8824   $9.88   $9.90   $9.90  
  Purchase #4 $202.95   12.553%   $228.4263   $228.43   $228.45   $228.40  
  Purchase #5 $95.77   12.869%   $108.0946   $108.09   $108.10   $108.10  
  Purchase #6 $104.29   6.233%   $110.7904   $110.79   $110.80   $110.80  
  Purchase #7 $59.43   4.792%   $62.2779   $62.28   $62.30   $62.30  
  7 purchase totals = $718.23       $791.9603   $791.96   $792.00   $792.00