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 $221.95   13.506%   $251.9266   $251.93   $251.95   $251.90  
  Purchase #2 $152.39   3.457%   $157.6581   $157.66   $157.65   $157.70  
  Purchase #3 $65.85   3.479%   $68.1409   $68.14   $68.15   $68.10  
  Purchase #4 $237.40   9.636%   $260.2759   $260.28   $260.30   $260.30  
  Purchase #5 $66.86   6.775%   $71.3898   $71.39   $71.40   $71.40  
  Purchase #6 $250.60   11.848%   $280.2911   $280.29   $280.30   $280.30  
  Purchase #7 $194.86   12.497%   $219.2117   $219.21   $219.20   $219.20  
  7 purchase totals = $1,189.91       $1,308.8941   $1,308.90   $1,308.95   $1,308.90