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 $86.29   8.269%   $93.4253   $93.43   $93.45   $93.40  
  Purchase #2 $40.63   13.345%   $46.0521   $46.05   $46.05   $46.10  
  Purchase #3 $103.29   11.160%   $114.8172   $114.82   $114.80   $114.80  
  Purchase #4 $93.34   9.234%   $101.959   $101.96   $101.95   $102.00  
  Purchase #5 $92.80   9.220%   $101.3562   $101.36   $101.35   $101.40  
  Purchase #6 $114.79   4.735%   $120.2253   $120.23   $120.25   $120.20  
  Purchase #7 $169.64   10.650%   $187.7067   $187.71   $187.70   $187.70  
  7 purchase totals = $700.78       $765.5418   $765.56   $765.55   $765.60