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 $67.97   8.725%   $73.9004   $73.90   $73.90   $73.90  
  Purchase #2 $221.69   11.603%   $247.4127   $247.41   $247.40   $247.40  
  Purchase #3 $19.36   5.282%   $20.3826   $20.38   $20.40   $20.40  
  Purchase #4 $68.36   5.469%   $72.0986   $72.10   $72.10   $72.10  
  Purchase #5 $93.64   9.807%   $102.8233   $102.82   $102.80   $102.80  
  Purchase #6 $221.91   8.108%   $239.9025   $239.90   $239.90   $239.90  
  Purchase #7 $104.50   11.422%   $116.436   $116.44   $116.45   $116.40  
  7 purchase totals = $797.43       $872.9561   $872.95   $872.95   $872.90