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 $64.83   10.532%   $71.6579   $71.66   $71.65   $71.70  
  Purchase #2 $151.43   9.867%   $166.3716   $166.37   $166.35   $166.40  
  Purchase #3 $55.76   11.552%   $62.2014   $62.20   $62.20   $62.20  
  Purchase #4 $206.35   12.796%   $232.7545   $232.75   $232.75   $232.80  
  Purchase #5 $154.61   5.172%   $162.6064   $162.61   $162.60   $162.60  
  Purchase #6 $215.75   6.297%   $229.3358   $229.34   $229.35   $229.30  
  Purchase #7 $21.51   11.738%   $24.0348   $24.03   $24.05   $24.00  
  7 purchase totals = $870.24       $948.9624   $948.96   $948.95   $949.00