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 $208.47   12.717%   $234.9811   $234.98   $235.00   $235.00  
  Purchase #2 $121.44   7.751%   $130.8528   $130.85   $130.85   $130.90  
  Purchase #3 $14.28   10.525%   $15.783   $15.78   $15.80   $15.80  
  Purchase #4 $97.49   10.749%   $107.9692   $107.97   $107.95   $108.00  
  Purchase #5 $169.85   7.382%   $182.3883   $182.39   $182.40   $182.40  
  Purchase #6 $82.66   11.346%   $92.0386   $92.04   $92.05   $92.00  
  Purchase #7 $147.69   13.786%   $168.0505   $168.05   $168.05   $168.10  
  7 purchase totals = $841.88       $932.0635   $932.06   $932.10   $932.20