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 $208.33   12.739%   $234.8692   $234.87   $234.85   $234.90  
  Purchase #2 $106.53   6.426%   $113.3756   $113.38   $113.40   $113.40  
  Purchase #3 $105.70   5.667%   $111.69   $111.69   $111.70   $111.70  
  Purchase #4 $52.80   8.679%   $57.3825   $57.38   $57.40   $57.40  
  Purchase #5 $239.42   7.761%   $258.0014   $258.00   $258.00   $258.00  
  Purchase #6 $15.45   5.333%   $16.2739   $16.27   $16.25   $16.30  
  Purchase #7 $84.62   9.452%   $92.6183   $92.62   $92.60   $92.60  
  7 purchase totals = $812.85       $884.2109   $884.21   $884.20   $884.30