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 $206.31   9.838%   $226.6068   $226.61   $226.60   $226.60  
  Purchase #2 $42.86   7.173%   $45.9343   $45.93   $45.95   $45.90  
  Purchase #3 $43.80   12.740%   $49.3801   $49.38   $49.40   $49.40  
  Purchase #4 $12.73   4.523%   $13.3058   $13.31   $13.30   $13.30  
  Purchase #5 $72.71   5.247%   $76.5251   $76.53   $76.55   $76.50  
  Purchase #6 $217.97   12.592%   $245.4168   $245.42   $245.40   $245.40  
  Purchase #7 $101.39   9.369%   $110.8892   $110.89   $110.90   $110.90  
  7 purchase totals = $697.77       $768.0581   $768.07   $768.10   $768.00