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 $75.42   10.657%   $83.4575   $83.46   $83.45   $83.50  
  Purchase #2 $207.49   7.834%   $223.7448   $223.74   $223.75   $223.70  
  Purchase #3 $96.91   8.249%   $104.9041   $104.90   $104.90   $104.90  
  Purchase #4 $214.73   3.303%   $221.8225   $221.82   $221.80   $221.80  
  Purchase #5 $21.64   5.136%   $22.7514   $22.75   $22.75   $22.80  
  Purchase #6 $38.77   7.585%   $41.7107   $41.71   $41.70   $41.70  
  Purchase #7 $242.61   5.203%   $255.233   $255.23   $255.25   $255.20  
  7 purchase totals = $897.57       $953.6240   $953.61   $953.60   $953.60