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	$100.61	8.274%	$108.9345	$108.93	$108.95	$108.90
Purchase #2	$234.88	7.164%	$251.7068	$251.71	$251.70	$251.70
Purchase #3	$174.70	11.480%	$194.7556	$194.76	$194.75	$194.80
Purchase #4	$130.93	11.527%	$146.0223	$146.02	$146.00	$146.00
Purchase #5	$200.83	11.304%	$223.5318	$223.53	$223.55	$223.50
Purchase #6	$17.89	3.133%	$18.4505	$18.45	$18.45	$18.50
Purchase #7	$209.31	9.173%	$228.51	$228.51	$228.50	$228.50
7 purchase totals =	$1,069.15		$1,171.9115	$1,171.91	$1,171.90	$1,171.90