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	$78.78	3.673%	$81.6736	$81.67	$81.65	$81.70
Purchase #2	$51.76	3.220%	$53.4267	$53.43	$53.45	$53.40
Purchase #3	$129.89	13.117%	$146.9277	$146.93	$146.95	$146.90
Purchase #4	$226.60	9.420%	$247.9457	$247.95	$247.95	$247.90
Purchase #5	$85.31	13.218%	$96.5863	$96.59	$96.60	$96.60
Purchase #6	$34.52	7.747%	$37.1943	$37.19	$37.20	$37.20
Purchase #7	$217.95	9.325%	$238.2738	$238.27	$238.25	$238.30
7 purchase totals =	$824.81		$902.0281	$902.03	$902.05	$902.00