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	$231.89	11.582%	$258.7475	$258.75	$258.75	$258.70
Purchase #2	$12.49	4.445%	$13.0452	$13.05	$13.05	$13.00
Purchase #3	$86.55	3.831%	$89.8657	$89.87	$89.85	$89.90
Purchase #4	$54.95	9.149%	$59.9774	$59.98	$60.00	$60.00
Purchase #5	$229.72	10.767%	$254.454	$254.45	$254.45	$254.50
Purchase #6	$88.79	12.105%	$99.538	$99.54	$99.55	$99.50
Purchase #7	$66.44	7.224%	$71.2396	$71.24	$71.25	$71.20
7 purchase totals =	$770.83		$846.8674	$846.88	$846.90	$846.80