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 $11.94   8.369%   $12.9393   $12.94   $12.95   $12.90  
  Purchase #2 $242.27   6.832%   $258.8219   $258.82   $258.80   $258.80  
  Purchase #3 $64.98   13.510%   $73.7588   $73.76   $73.75   $73.80  
  Purchase #4 $194.80   5.329%   $205.1809   $205.18   $205.20   $205.20  
  Purchase #5 $144.39   4.760%   $151.263   $151.26   $151.25   $151.30  
  Purchase #6 $190.49   11.849%   $213.0612   $213.06   $213.05   $213.10  
  Purchase #7 $34.77   3.563%   $36.0089   $36.01   $36.00   $36.00  
  7 purchase totals = $883.64       $951.0340   $951.03   $951.00   $951.10