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 $110.98   12.776%   $125.1588   $125.16   $125.15   $125.20  
  Purchase #2 $131.48   8.362%   $142.4744   $142.47   $142.45   $142.50  
  Purchase #3 $23.26   6.482%   $24.7677   $24.77   $24.75   $24.80  
  Purchase #4 $222.70   5.849%   $235.7257   $235.73   $235.75   $235.70  
  Purchase #5 $74.78   10.185%   $82.3963   $82.40   $82.40   $82.40  
  Purchase #6 $166.25   8.435%   $180.2732   $180.27   $180.25   $180.30  
  Purchase #7 $142.99   13.499%   $162.2922   $162.29   $162.30   $162.30  
  7 purchase totals = $872.44       $953.0883   $953.09   $953.05   $953.20