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 $134.83   12.713%   $151.9709   $151.97   $151.95   $152.00  
  Purchase #2 $234.97   11.441%   $261.8529   $261.85   $261.85   $261.90  
  Purchase #3 $246.35   9.185%   $268.9772   $268.98   $269.00   $269.00  
  Purchase #4 $166.26   11.387%   $185.192   $185.19   $185.20   $185.20  
  Purchase #5 $190.75   8.128%   $206.2542   $206.25   $206.25   $206.30  
  Purchase #6 $164.79   13.761%   $187.4668   $187.47   $187.45   $187.50  
  Purchase #7 $245.51   11.580%   $273.9401   $273.94   $273.95   $273.90  
  7 purchase totals = $1,383.46       $1,535.6541   $1,535.65   $1,535.65   $1,535.80