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 $11.69   10.681%   $12.9386   $12.94   $12.95   $12.90  
  Purchase #2 $118.66   12.636%   $133.6539   $133.65   $133.65   $133.70  
  Purchase #3 $60.90   13.288%   $68.9924   $68.99   $69.00   $69.00  
  Purchase #4 $105.99   12.794%   $119.5504   $119.55   $119.55   $119.60  
  Purchase #5 $6.45   12.485%   $7.2553   $7.26   $7.25   $7.30  
  Purchase #6 $241.77   9.267%   $264.1748   $264.17   $264.15   $264.20  
  Purchase #7 $197.43   13.712%   $224.5016   $224.50   $224.50   $224.50  
  7 purchase totals = $742.89       $831.0670   $831.06   $831.05   $831.20