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 $52.47   11.428%   $58.4663   $58.47   $58.45   $58.50  
  Purchase #2 $102.36   13.267%   $115.9401   $115.94   $115.95   $115.90  
  Purchase #3 $110.94   13.104%   $125.4776   $125.48   $125.50   $125.50  
  Purchase #4 $89.77   6.776%   $95.8528   $95.85   $95.85   $95.90  
  Purchase #5 $166.41   6.845%   $177.8008   $177.80   $177.80   $177.80  
  Purchase #6 $19.64   4.575%   $20.5385   $20.54   $20.55   $20.50  
  Purchase #7 $55.68   10.309%   $61.4201   $61.42   $61.40   $61.40  
  7 purchase totals = $597.27       $655.4962   $655.50   $655.50   $655.50