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 $98.87   5.849%   $104.6529   $104.65   $104.65   $104.70  
  Purchase #2 $53.50   7.606%   $57.5692   $57.57   $57.55   $57.60  
  Purchase #3 $22.86   3.296%   $23.6135   $23.61   $23.60   $23.60  
  Purchase #4 $72.67   8.345%   $78.7343   $78.73   $78.75   $78.70  
  Purchase #5 $94.47   10.456%   $104.3478   $104.35   $104.35   $104.30  
  Purchase #6 $177.35   8.845%   $193.0366   $193.04   $193.05   $193.00  
  Purchase #7 $59.69   4.869%   $62.5963   $62.60   $62.60   $62.60  
  7 purchase totals = $579.41       $624.5506   $624.55   $624.55   $624.50