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 $86.47   11.358%   $96.2913   $96.29   $96.30   $96.30  
  Purchase #2 $166.76   7.420%   $179.1336   $179.13   $179.15   $179.10  
  Purchase #3 $193.32   11.168%   $214.91   $214.91   $214.90   $214.90  
  Purchase #4 $152.55   5.253%   $160.5635   $160.56   $160.55   $160.60  
  Purchase #5 $234.25   11.702%   $261.6619   $261.66   $261.65   $261.70  
  Purchase #6 $139.87   3.165%   $144.2969   $144.30   $144.30   $144.30  
  Purchase #7 $188.47   7.125%   $201.8985   $201.90   $201.90   $201.90  
  7 purchase totals = $1,161.69       $1,258.7557   $1,258.75   $1,258.75   $1,258.80