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 $57.92   8.224%   $62.6833   $62.68   $62.70   $62.70  
  Purchase #2 $202.48   9.375%   $221.4625   $221.46   $221.45   $221.50  
  Purchase #3 $156.29   3.248%   $161.3663   $161.37   $161.35   $161.40  
  Purchase #4 $180.42   8.721%   $196.1544   $196.15   $196.15   $196.20  
  Purchase #5 $79.63   6.422%   $84.7438   $84.74   $84.75   $84.70  
  Purchase #6 $182.30   4.142%   $189.8509   $189.85   $189.85   $189.90  
  Purchase #7 $250.52   11.726%   $279.896   $279.90   $279.90   $279.90  
  7 purchase totals = $1,109.56       $1,196.1572   $1,196.15   $1,196.15   $1,196.30