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 $230.43   6.631%   $245.7098   $245.71   $245.70   $245.70  
  Purchase #2 $101.90   12.505%   $114.6426   $114.64   $114.65   $114.60  
  Purchase #3 $155.84   6.634%   $166.1784   $166.18   $166.20   $166.20  
  Purchase #4 $195.51   7.215%   $209.616   $209.62   $209.60   $209.60  
  Purchase #5 $48.61   8.207%   $52.5994   $52.60   $52.60   $52.60  
  Purchase #6 $59.47   7.727%   $64.0652   $64.07   $64.05   $64.10  
  Purchase #7 $12.56   7.428%   $13.493   $13.49   $13.50   $13.50  
  7 purchase totals = $804.32       $866.3044   $866.31   $866.30   $866.30