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 $250.53   11.518%   $279.386   $279.39   $279.40   $279.40  
  Purchase #2 $224.41   6.263%   $238.4648   $238.46   $238.45   $238.50  
  Purchase #3 $217.77   8.735%   $236.7922   $236.79   $236.80   $236.80  
  Purchase #4 $5.41   6.184%   $5.7446   $5.74   $5.75   $5.70  
  Purchase #5 $148.28   11.451%   $165.2595   $165.26   $165.25   $165.30  
  Purchase #6 $91.45   12.630%   $103.0001   $103.00   $103.00   $103.00  
  Purchase #7 $244.38   9.288%   $267.078   $267.08   $267.10   $267.10  
  7 purchase totals = $1,182.23       $1,295.7252   $1,295.72   $1,295.75   $1,295.80