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 $94.81   3.746%   $98.3616   $98.36   $98.35   $98.40  
  Purchase #2 $194.28   6.462%   $206.8344   $206.83   $206.85   $206.80  
  Purchase #3 $113.75   5.465%   $119.9664   $119.97   $119.95   $120.00  
  Purchase #4 $96.68   7.244%   $103.6835   $103.68   $103.70   $103.70  
  Purchase #5 $190.32   3.826%   $197.6016   $197.60   $197.60   $197.60  
  Purchase #6 $160.97   13.164%   $182.1601   $182.16   $182.15   $182.20  
  Purchase #7 $29.39   10.281%   $32.4116   $32.41   $32.40   $32.40  
  7 purchase totals = $880.20       $941.0192   $941.01   $941.00   $941.10