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 $90.66   3.270%   $93.6246   $93.62   $93.60   $93.60  
  Purchase #2 $195.89   10.306%   $216.0784   $216.08   $216.10   $216.10  
  Purchase #3 $115.86   8.436%   $125.6339   $125.63   $125.65   $125.60  
  Purchase #4 $98.87   5.679%   $104.4848   $104.48   $104.50   $104.50  
  Purchase #5 $108.89   7.579%   $117.1428   $117.14   $117.15   $117.10  
  Purchase #6 $131.40   11.117%   $146.0077   $146.01   $146.00   $146.00  
  Purchase #7 $230.65   12.456%   $259.3798   $259.38   $259.40   $259.40  
  7 purchase totals = $972.22       $1,062.3520   $1,062.34   $1,062.40   $1,062.30