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 $62.44   9.766%   $68.5379   $68.54   $68.55   $68.50  
  Purchase #2 $71.70   11.212%   $79.739   $79.74   $79.75   $79.70  
  Purchase #3 $73.78   5.785%   $78.0482   $78.05   $78.05   $78.00  
  Purchase #4 $21.51   3.459%   $22.254   $22.25   $22.25   $22.30  
  Purchase #5 $219.30   6.420%   $233.3791   $233.38   $233.40   $233.40  
  Purchase #6 $11.74   3.771%   $12.1827   $12.18   $12.20   $12.20  
  Purchase #7 $60.66   11.579%   $67.6838   $67.68   $67.70   $67.70  
  7 purchase totals = $521.13       $561.8247   $561.82   $561.90   $561.80