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 $58.82   11.458%   $65.5596   $65.56   $65.55   $65.60  
  Purchase #2 $237.54   11.296%   $264.3725   $264.37   $264.35   $264.40  
  Purchase #3 $168.45   13.410%   $191.0391   $191.04   $191.05   $191.00  
  Purchase #4 $15.53   11.691%   $17.3456   $17.35   $17.35   $17.30  
  Purchase #5 $117.45   13.644%   $133.4749   $133.47   $133.45   $133.50  
  Purchase #6 $103.87   9.266%   $113.4946   $113.49   $113.50   $113.50  
  Purchase #7 $119.44   5.611%   $126.1418   $126.14   $126.15   $126.10  
  7 purchase totals = $821.10       $911.4281   $911.42   $911.40   $911.40