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 $60.34   13.440%   $68.4497   $68.45   $68.45   $68.40  
  Purchase #2 $64.46   9.688%   $70.7049   $70.70   $70.70   $70.70  
  Purchase #3 $174.89   9.648%   $191.7634   $191.76   $191.75   $191.80  
  Purchase #4 $6.59   8.667%   $7.1612   $7.16   $7.15   $7.20  
  Purchase #5 $246.50   13.754%   $280.4036   $280.40   $280.40   $280.40  
  Purchase #6 $26.53   6.333%   $28.2101   $28.21   $28.20   $28.20  
  Purchase #7 $207.36   5.435%   $218.63   $218.63   $218.65   $218.60  
  7 purchase totals = $786.67       $865.3229   $865.31   $865.30   $865.30