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 $58.63   7.509%   $63.0325   $63.03   $63.05   $63.00  
  Purchase #2 $131.40   5.869%   $139.1119   $139.11   $139.10   $139.10  
  Purchase #3 $191.46   6.530%   $203.9623   $203.96   $203.95   $204.00  
  Purchase #4 $19.26   5.268%   $20.2746   $20.27   $20.25   $20.30  
  Purchase #5 $73.55   7.313%   $78.9287   $78.93   $78.95   $78.90  
  Purchase #6 $149.87   5.753%   $158.492   $158.49   $158.50   $158.50  
  Purchase #7 $78.87   8.668%   $85.7065   $85.71   $85.70   $85.70  
  7 purchase totals = $703.04       $749.5085   $749.50   $749.50   $749.50