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 $58.44   9.480%   $63.9801   $63.98   $64.00   $64.00  
  Purchase #2 $187.35   11.702%   $209.2737   $209.27   $209.25   $209.30  
  Purchase #3 $146.70   9.305%   $160.3504   $160.35   $160.35   $160.40  
  Purchase #4 $103.85   6.152%   $110.2389   $110.24   $110.25   $110.20  
  Purchase #5 $224.81   6.533%   $239.4968   $239.50   $239.50   $239.50  
  Purchase #6 $233.74   5.828%   $247.3624   $247.36   $247.35   $247.40  
  Purchase #7 $195.27   9.206%   $213.2466   $213.25   $213.25   $213.20  
  7 purchase totals = $1,150.16       $1,243.9489   $1,243.95   $1,243.95   $1,244.00