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 $71.26   3.292%   $73.6059   $73.61   $73.60   $73.60  
  Purchase #2 $46.63   10.829%   $51.6796   $51.68   $51.70   $51.70  
  Purchase #3 $71.54   4.614%   $74.8409   $74.84   $74.85   $74.80  
  Purchase #4 $93.86   5.229%   $98.7679   $98.77   $98.75   $98.80  
  Purchase #5 $139.97   4.830%   $146.7306   $146.73   $146.75   $146.70  
  Purchase #6 $174.38   3.669%   $180.778   $180.78   $180.80   $180.80  
  Purchase #7 $205.42   4.341%   $214.3373   $214.34   $214.35   $214.30  
  7 purchase totals = $803.06       $840.7402   $840.75   $840.80   $840.70