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 $55.36   3.602%   $57.3541   $57.35   $57.35   $57.40  
  Purchase #2 $87.66   9.350%   $95.8562   $95.86   $95.85   $95.90  
  Purchase #3 $160.38   5.647%   $169.4367   $169.44   $169.45   $169.40  
  Purchase #4 $240.58   11.298%   $267.7607   $267.76   $267.75   $267.80  
  Purchase #5 $221.43   8.318%   $239.8485   $239.85   $239.85   $239.80  
  Purchase #6 $152.39   7.703%   $164.1286   $164.13   $164.15   $164.10  
  Purchase #7 $47.91   3.707%   $49.686   $49.69   $49.70   $49.70  
  7 purchase totals = $965.71       $1,044.0708   $1,044.08   $1,044.10   $1,044.10