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	$49.31	4.313%	$51.4367	$51.44	$51.45	$51.40
Purchase #2	$71.38	11.834%	$79.8271	$79.83	$79.85	$79.80
Purchase #3	$148.29	11.663%	$165.5851	$165.59	$165.60	$165.60
Purchase #4	$34.68	10.701%	$38.3911	$38.39	$38.40	$38.40
Purchase #5	$172.51	10.832%	$191.1963	$191.20	$191.20	$191.20
Purchase #6	$117.89	11.300%	$131.2116	$131.21	$131.20	$131.20
Purchase #7	$140.53	4.401%	$146.7147	$146.71	$146.70	$146.70
7 purchase totals =	$734.59		$804.3626	$804.37	$804.40	$804.30