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 $60.44   4.513%   $63.1677   $63.17   $63.15   $63.20  
  Purchase #2 $161.50   9.352%   $176.6035   $176.60   $176.60   $176.60  
  Purchase #3 $83.53   3.607%   $86.5429   $86.54   $86.55   $86.50  
  Purchase #4 $63.69   12.566%   $71.6933   $71.69   $71.70   $71.70  
  Purchase #5 $68.71   10.326%   $75.805   $75.81   $75.80   $75.80  
  Purchase #6 $234.99   4.248%   $244.9724   $244.97   $244.95   $245.00  
  Purchase #7 $68.97   4.769%   $72.2592   $72.26   $72.25   $72.30  
  7 purchase totals = $741.83       $791.0440   $791.04   $791.00   $791.10