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 $47.33   6.572%   $50.4405   $50.44   $50.45   $50.40  
  Purchase #2 $200.35   7.413%   $215.2019   $215.20   $215.20   $215.20  
  Purchase #3 $182.28   12.451%   $204.9757   $204.98   $205.00   $205.00  
  Purchase #4 $61.91   3.119%   $63.841   $63.84   $63.85   $63.80  
  Purchase #5 $245.31   4.201%   $255.6155   $255.62   $255.60   $255.60  
  Purchase #6 $101.50   12.440%   $114.1266   $114.13   $114.15   $114.10  
  Purchase #7 $26.95   6.667%   $28.7468   $28.75   $28.75   $28.70  
  7 purchase totals = $865.63       $932.9480   $932.96   $933.00   $932.80