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 $81.32   4.798%   $85.2217   $85.22   $85.20   $85.20  
  Purchase #2 $133.79   9.839%   $146.9536   $146.95   $146.95   $147.00  
  Purchase #3 $222.64   4.616%   $232.9171   $232.92   $232.90   $232.90  
  Purchase #4 $139.71   10.168%   $153.9157   $153.92   $153.90   $153.90  
  Purchase #5 $180.74   8.416%   $195.9511   $195.95   $195.95   $196.00  
  Purchase #6 $151.93   4.429%   $158.659   $158.66   $158.65   $158.70  
  Purchase #7 $26.40   9.314%   $28.8589   $28.86   $28.85   $28.90  
  7 purchase totals = $936.53       $1,002.4771   $1,002.48   $1,002.40   $1,002.60