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 $55.29   8.802%   $60.1566   $60.16   $60.15   $60.20  
  Purchase #2 $46.57   11.266%   $51.8166   $51.82   $51.80   $51.80  
  Purchase #3 $119.40   10.562%   $132.011   $132.01   $132.00   $132.00  
  Purchase #4 $119.89   8.672%   $130.2869   $130.29   $130.30   $130.30  
  Purchase #5 $87.59   12.857%   $98.8514   $98.85   $98.85   $98.90  
  Purchase #6 $186.74   11.281%   $207.8061   $207.81   $207.80   $207.80  
  Purchase #7 $89.59   12.770%   $101.0306   $101.03   $101.05   $101.00  
  7 purchase totals = $705.07       $781.9592   $781.97   $781.95   $782.00