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	$105.70	6.726%	$112.8094	$112.81	$112.80	$112.80
Purchase #2	$81.94	5.519%	$86.4623	$86.46	$86.45	$86.50
Purchase #3	$150.39	6.432%	$160.0631	$160.06	$160.05	$160.10
Purchase #4	$155.93	3.776%	$161.8179	$161.82	$161.80	$161.80
Purchase #5	$18.78	11.647%	$20.9673	$20.97	$20.95	$21.00
Purchase #6	$93.93	11.386%	$104.6249	$104.62	$104.60	$104.60
Purchase #7	$187.53	4.740%	$196.4189	$196.42	$196.40	$196.40
7 purchase totals =	$794.20		$843.1638	$843.16	$843.05	$843.20