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 $234.98   12.858%   $265.1937   $265.19   $265.20   $265.20  
  Purchase #2 $131.62   11.209%   $146.3733   $146.37   $146.35   $146.40  
  Purchase #3 $157.99   6.807%   $168.7444   $168.74   $168.75   $168.70  
  Purchase #4 $76.66   11.415%   $85.4107   $85.41   $85.40   $85.40  
  Purchase #5 $159.73   12.616%   $179.8815   $179.88   $179.90   $179.90  
  Purchase #6 $63.89   9.373%   $69.8784   $69.88   $69.90   $69.90  
  Purchase #7 $167.89   6.165%   $178.2404   $178.24   $178.25   $178.20  
  7 purchase totals = $992.76       $1,093.7224   $1,093.71   $1,093.75   $1,093.70