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 $88.61   5.779%   $93.7308   $93.73   $93.75   $93.70  
  Purchase #2 $73.33   13.374%   $83.1372   $83.14   $83.15   $83.10  
  Purchase #3 $23.71   3.612%   $24.5664   $24.57   $24.55   $24.60  
  Purchase #4 $182.93   6.819%   $195.404   $195.40   $195.40   $195.40  
  Purchase #5 $103.99   12.744%   $117.2425   $117.24   $117.25   $117.20  
  Purchase #6 $58.69   7.118%   $62.8676   $62.87   $62.85   $62.90  
  Purchase #7 $250.77   9.124%   $273.6503   $273.65   $273.65   $273.70  
  7 purchase totals = $782.03       $850.5988   $850.60   $850.60   $850.60