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 $207.56   3.791%   $215.4286   $215.43   $215.45   $215.40  
  Purchase #2 $237.40   8.677%   $257.9992   $258.00   $258.00   $258.00  
  Purchase #3 $42.50   12.613%   $47.8605   $47.86   $47.85   $47.90  
  Purchase #4 $60.47   4.690%   $63.306   $63.31   $63.30   $63.30  
  Purchase #5 $87.49   7.321%   $93.8951   $93.90   $93.90   $93.90  
  Purchase #6 $59.82   10.223%   $65.9354   $65.94   $65.95   $65.90  
  Purchase #7 $96.38   4.798%   $101.0043   $101.00   $101.00   $101.00  
  7 purchase totals = $791.62       $845.4291   $845.44   $845.45   $845.40