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 $226.38   12.293%   $254.2089   $254.21   $254.20   $254.20  
  Purchase #2 $30.74   10.669%   $34.0197   $34.02   $34.00   $34.00  
  Purchase #3 $103.82   12.213%   $116.4995   $116.50   $116.50   $116.50  
  Purchase #4 $169.73   9.202%   $185.3486   $185.35   $185.35   $185.30  
  Purchase #5 $37.93   13.330%   $42.9861   $42.99   $43.00   $43.00  
  Purchase #6 $42.54   13.569%   $48.3123   $48.31   $48.30   $48.30  
  Purchase #7 $205.90   13.396%   $233.4824   $233.48   $233.50   $233.50  
  7 purchase totals = $817.04       $914.8575   $914.86   $914.85   $914.80