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 $245.65   6.631%   $261.9391   $261.94   $261.95   $261.90  
  Purchase #2 $131.40   11.708%   $146.7843   $146.78   $146.80   $146.80  
  Purchase #3 $73.67   4.478%   $76.9689   $76.97   $76.95   $77.00  
  Purchase #4 $69.47   9.310%   $75.9377   $75.94   $75.95   $75.90  
  Purchase #5 $74.74   8.294%   $80.9389   $80.94   $80.95   $80.90  
  Purchase #6 $26.88   5.110%   $28.2536   $28.25   $28.25   $28.30  
  Purchase #7 $75.33   9.838%   $82.741   $82.74   $82.75   $82.70  
  7 purchase totals = $697.14       $753.5635   $753.56   $753.60   $753.50