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 $42.66   5.259%   $44.9035   $44.90   $44.90   $44.90  
  Purchase #2 $244.94   6.626%   $261.1697   $261.17   $261.15   $261.20  
  Purchase #3 $221.30   6.173%   $234.9608   $234.96   $234.95   $235.00  
  Purchase #4 $222.64   4.799%   $233.3245   $233.32   $233.30   $233.30  
  Purchase #5 $118.97   8.588%   $129.1871   $129.19   $129.20   $129.20  
  Purchase #6 $116.55   3.219%   $120.3017   $120.30   $120.30   $120.30  
  Purchase #7 $229.47   13.856%   $261.2654   $261.27   $261.25   $261.30  
  7 purchase totals = $1,196.53       $1,285.1127   $1,285.11   $1,285.05   $1,285.20