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 $109.33   9.112%   $119.2921   $119.29   $119.30   $119.30  
  Purchase #2 $151.68   4.616%   $158.6815   $158.68   $158.70   $158.70  
  Purchase #3 $34.50   11.819%   $38.5776   $38.58   $38.60   $38.60  
  Purchase #4 $213.29   13.638%   $242.3785   $242.38   $242.40   $242.40  
  Purchase #5 $184.82   5.378%   $194.7596   $194.76   $194.75   $194.80  
  Purchase #6 $98.55   13.181%   $111.5399   $111.54   $111.55   $111.50  
  Purchase #7 $176.26   10.319%   $194.4483   $194.45   $194.45   $194.40  
  7 purchase totals = $968.43       $1,059.6775   $1,059.68   $1,059.75   $1,059.70