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 $167.62   4.173%   $174.6148   $174.61   $174.60   $174.60  
  Purchase #2 $134.83   10.578%   $149.0923   $149.09   $149.10   $149.10  
  Purchase #3 $63.29   13.622%   $71.9114   $71.91   $71.90   $71.90  
  Purchase #4 $53.76   6.481%   $57.2442   $57.24   $57.25   $57.20  
  Purchase #5 $105.58   10.155%   $116.3016   $116.30   $116.30   $116.30  
  Purchase #6 $60.35   5.179%   $63.4755   $63.48   $63.50   $63.50  
  Purchase #7 $244.73   11.534%   $272.9572   $272.96   $272.95   $273.00  
  7 purchase totals = $830.16       $905.5970   $905.59   $905.60   $905.60