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 $65.95   9.860%   $72.4527   $72.45   $72.45   $72.50  
  Purchase #2 $233.63   5.283%   $245.9727   $245.97   $245.95   $246.00  
  Purchase #3 $241.40   7.276%   $258.9643   $258.96   $258.95   $259.00  
  Purchase #4 $58.42   6.454%   $62.1904   $62.19   $62.20   $62.20  
  Purchase #5 $18.83   8.385%   $20.4089   $20.41   $20.40   $20.40  
  Purchase #6 $66.84   10.769%   $74.038   $74.04   $74.05   $74.00  
  Purchase #7 $93.51   10.118%   $102.9713   $102.97   $102.95   $103.00  
  7 purchase totals = $778.58       $836.9983   $836.99   $836.95   $837.10