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 $78.25   3.621%   $81.0834   $81.08   $81.10   $81.10  
  Purchase #2 $139.51   9.390%   $152.61   $152.61   $152.60   $152.60  
  Purchase #3 $139.36   13.827%   $158.6293   $158.63   $158.65   $158.60  
  Purchase #4 $185.39   10.108%   $204.1292   $204.13   $204.15   $204.10  
  Purchase #5 $31.78   12.296%   $35.6877   $35.69   $35.70   $35.70  
  Purchase #6 $141.34   5.380%   $148.9441   $148.94   $148.95   $148.90  
  Purchase #7 $118.32   7.259%   $126.9088   $126.91   $126.90   $126.90  
  7 purchase totals = $833.95       $907.9925   $907.99   $908.05   $907.90