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 $235.37   7.719%   $253.5382   $253.54   $253.55   $253.50  
  Purchase #2 $191.97   4.116%   $199.8715   $199.87   $199.85   $199.90  
  Purchase #3 $83.42   12.731%   $94.0402   $94.04   $94.05   $94.00  
  Purchase #4 $210.62   12.175%   $236.263   $236.26   $236.25   $236.30  
  Purchase #5 $107.71   12.514%   $121.1888   $121.19   $121.20   $121.20  
  Purchase #6 $209.77   5.375%   $221.0451   $221.05   $221.05   $221.00  
  Purchase #7 $169.66   7.809%   $182.9087   $182.91   $182.90   $182.90  
  7 purchase totals = $1,208.52       $1,308.8555   $1,308.86   $1,308.85   $1,308.80