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 $72.51   3.105%   $74.7614   $74.76   $74.75   $74.80  
  Purchase #2 $179.84   8.832%   $195.7235   $195.72   $195.70   $195.70  
  Purchase #3 $159.90   7.555%   $171.9804   $171.98   $172.00   $172.00  
  Purchase #4 $245.56   5.462%   $258.9725   $258.97   $258.95   $259.00  
  Purchase #5 $233.37   8.574%   $253.3791   $253.38   $253.40   $253.40  
  Purchase #6 $176.54   7.574%   $189.9111   $189.91   $189.90   $189.90  
  Purchase #7 $80.92   11.688%   $90.3779   $90.38   $90.40   $90.40  
  7 purchase totals = $1,148.64       $1,235.1059   $1,235.10   $1,235.10   $1,235.20