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 $135.27   13.722%   $153.8317   $153.83   $153.85   $153.80  
  Purchase #2 $46.59   11.246%   $51.8295   $51.83   $51.85   $51.80  
  Purchase #3 $60.38   6.691%   $64.42   $64.42   $64.40   $64.40  
  Purchase #4 $43.89   8.461%   $47.6035   $47.60   $47.60   $47.60  
  Purchase #5 $195.50   6.259%   $207.7363   $207.74   $207.75   $207.70  
  Purchase #6 $204.59   4.684%   $214.173   $214.17   $214.15   $214.20  
  Purchase #7 $21.72   7.435%   $23.3349   $23.33   $23.35   $23.30  
  7 purchase totals = $707.94       $762.9289   $762.92   $762.95   $762.80