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 $68.67   6.583%   $73.1905   $73.19   $73.20   $73.20  
  Purchase #2 $109.79   8.559%   $119.1869   $119.19   $119.20   $119.20  
  Purchase #3 $83.92   8.860%   $91.3553   $91.36   $91.35   $91.40  
  Purchase #4 $248.73   4.344%   $259.5348   $259.53   $259.55   $259.50  
  Purchase #5 $26.75   5.299%   $28.1675   $28.17   $28.15   $28.20  
  Purchase #6 $135.81   3.805%   $140.9776   $140.98   $141.00   $141.00  
  Purchase #7 $247.42   10.775%   $274.0795   $274.08   $274.10   $274.10  
  7 purchase totals = $921.09       $986.4921   $986.50   $986.55   $986.60