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 $180.69   4.158%   $188.2031   $188.20   $188.20   $188.20  
  Purchase #2 $116.66   7.717%   $125.6627   $125.66   $125.65   $125.70  
  Purchase #3 $87.45   12.613%   $98.4801   $98.48   $98.50   $98.50  
  Purchase #4 $232.49   9.369%   $254.272   $254.27   $254.25   $254.30  
  Purchase #5 $212.74   3.841%   $220.9113   $220.91   $220.90   $220.90  
  Purchase #6 $243.53   12.161%   $273.1457   $273.15   $273.15   $273.10  
  Purchase #7 $221.91   11.677%   $247.8224   $247.82   $247.80   $247.80  
  7 purchase totals = $1,295.47       $1,408.4973   $1,408.49   $1,408.45   $1,408.50