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 $114.74   3.752%   $119.045   $119.05   $119.05   $119.00  
  Purchase #2 $237.90   8.686%   $258.564   $258.56   $258.55   $258.60  
  Purchase #3 $47.30   10.144%   $52.0981   $52.10   $52.10   $52.10  
  Purchase #4 $14.27   6.379%   $15.1803   $15.18   $15.20   $15.20  
  Purchase #5 $244.64   5.623%   $258.3961   $258.40   $258.40   $258.40  
  Purchase #6 $64.86   12.511%   $72.9746   $72.97   $72.95   $73.00  
  Purchase #7 $69.49   7.584%   $74.7601   $74.76   $74.75   $74.80  
  7 purchase totals = $793.20       $851.0182   $851.02   $851.00   $851.10