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 $86.93   7.612%   $93.5471   $93.55   $93.55   $93.50  
  Purchase #2 $210.46   8.502%   $228.3533   $228.35   $228.35   $228.40  
  Purchase #3 $96.71   13.135%   $109.4129   $109.41   $109.40   $109.40  
  Purchase #4 $158.63   11.300%   $176.5552   $176.56   $176.55   $176.60  
  Purchase #5 $188.42   7.632%   $202.8002   $202.80   $202.80   $202.80  
  Purchase #6 $109.95   10.610%   $121.6157   $121.62   $121.60   $121.60  
  Purchase #7 $26.33   10.663%   $29.1376   $29.14   $29.15   $29.10  
  7 purchase totals = $877.43       $961.4220   $961.43   $961.40   $961.40