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 $61.31   9.584%   $67.186   $67.19   $67.20   $67.20  
  Purchase #2 $213.75   3.369%   $220.9512   $220.95   $220.95   $221.00  
  Purchase #3 $162.58   7.549%   $174.8532   $174.85   $174.85   $174.90  
  Purchase #4 $250.56   4.322%   $261.3892   $261.39   $261.40   $261.40  
  Purchase #5 $26.78   3.846%   $27.81   $27.81   $27.80   $27.80  
  Purchase #6 $62.89   9.181%   $68.6639   $68.66   $68.65   $68.70  
  Purchase #7 $111.74   13.193%   $126.4819   $126.48   $126.50   $126.50  
  7 purchase totals = $889.61       $947.3354   $947.33   $947.35   $947.50