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 $44.96   7.529%   $48.345   $48.35   $48.35   $48.30  
  Purchase #2 $242.51   3.403%   $250.7626   $250.76   $250.75   $250.80  
  Purchase #3 $9.68   7.389%   $10.3953   $10.40   $10.40   $10.40  
  Purchase #4 $151.88   9.549%   $166.383   $166.38   $166.40   $166.40  
  Purchase #5 $24.58   7.192%   $26.3478   $26.35   $26.35   $26.30  
  Purchase #6 $86.32   11.126%   $95.924   $95.92   $95.90   $95.90  
  Purchase #7 $15.77   7.471%   $16.9482   $16.95   $16.95   $16.90  
  7 purchase totals = $575.70       $615.1059   $615.11   $615.10   $615.00