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 $244.65   9.342%   $267.5052   $267.51   $267.50   $267.50  
  Purchase #2 $42.94   5.691%   $45.3837   $45.38   $45.40   $45.40  
  Purchase #3 $61.34   10.536%   $67.8028   $67.80   $67.80   $67.80  
  Purchase #4 $213.62   10.509%   $236.0693   $236.07   $236.05   $236.10  
  Purchase #5 $169.93   5.449%   $179.1895   $179.19   $179.20   $179.20  
  Purchase #6 $121.76   11.566%   $135.8428   $135.84   $135.85   $135.80  
  Purchase #7 $238.74   13.693%   $271.4307   $271.43   $271.45   $271.40  
  7 purchase totals = $1,092.98       $1,203.2240   $1,203.22   $1,203.25   $1,203.20