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	$222.25	13.260%	$251.7204	$251.72	$251.70	$251.70
Purchase #2	$217.93	8.181%	$235.7589	$235.76	$235.75	$235.80
Purchase #3	$246.52	3.258%	$254.5516	$254.55	$254.55	$254.60
Purchase #4	$34.88	4.795%	$36.5525	$36.55	$36.55	$36.60
Purchase #5	$196.90	13.196%	$222.8829	$222.88	$222.90	$222.90
Purchase #6	$104.28	6.855%	$111.4284	$111.43	$111.45	$111.40
Purchase #7	$57.85	8.299%	$62.651	$62.65	$62.65	$62.70
7 purchase totals =	$1,080.61		$1,175.5457	$1,175.54	$1,175.55	$1,175.70