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 $246.94   3.649%   $255.9508   $255.95   $255.95   $256.00  
  Purchase #2 $132.40   11.486%   $147.6075   $147.61   $147.60   $147.60  
  Purchase #3 $204.35   4.560%   $213.6684   $213.67   $213.65   $213.70  
  Purchase #4 $222.39   4.422%   $232.2241   $232.22   $232.20   $232.20  
  Purchase #5 $97.66   9.234%   $106.6779   $106.68   $106.70   $106.70  
  Purchase #6 $150.28   4.473%   $157.002   $157.00   $157.00   $157.00  
  Purchase #7 $119.67   13.125%   $135.3767   $135.38   $135.40   $135.40  
  7 purchase totals = $1,173.69       $1,248.5074   $1,248.51   $1,248.50   $1,248.60