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 $105.94   9.251%   $115.7405   $115.74   $115.75   $115.70  
  Purchase #2 $183.72   12.154%   $206.0493   $206.05   $206.05   $206.00  
  Purchase #3 $64.30   3.396%   $66.4836   $66.48   $66.50   $66.50  
  Purchase #4 $240.96   5.380%   $253.9236   $253.92   $253.90   $253.90  
  Purchase #5 $225.42   9.545%   $246.9363   $246.94   $246.95   $246.90  
  Purchase #6 $14.41   13.346%   $16.3332   $16.33   $16.35   $16.30  
  Purchase #7 $71.95   6.422%   $76.5706   $76.57   $76.55   $76.60  
  7 purchase totals = $906.70       $982.0371   $982.03   $982.05   $981.90