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 $60.35   13.430%   $68.455   $68.46   $68.45   $68.50  
  Purchase #2 $6.26   5.157%   $6.5828   $6.58   $6.60   $6.60  
  Purchase #3 $6.70   8.370%   $7.2608   $7.26   $7.25   $7.30  
  Purchase #4 $86.99   8.434%   $94.3267   $94.33   $94.35   $94.30  
  Purchase #5 $44.85   13.562%   $50.9326   $50.93   $50.95   $50.90  
  Purchase #6 $157.48   13.330%   $178.4721   $178.47   $178.45   $178.50  
  Purchase #7 $26.71   8.130%   $28.8815   $28.88   $28.90   $28.90  
  7 purchase totals = $389.34       $434.9115   $434.91   $434.95   $435.00