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 $231.53   8.164%   $250.4321   $250.43   $250.45   $250.40  
  Purchase #2 $32.77   7.564%   $35.2487   $35.25   $35.25   $35.20  
  Purchase #3 $109.62   7.759%   $118.1254   $118.13   $118.15   $118.10  
  Purchase #4 $233.46   12.433%   $262.4861   $262.49   $262.50   $262.50  
  Purchase #5 $59.86   13.777%   $68.1069   $68.11   $68.10   $68.10  
  Purchase #6 $48.67   6.337%   $51.7542   $51.75   $51.75   $51.80  
  Purchase #7 $8.37   13.633%   $9.5111   $9.51   $9.50   $9.50  
  7 purchase totals = $724.28       $795.6645   $795.67   $795.70   $795.60