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	$223.55	4.843%	$234.3765	$234.38	$234.40	$234.40
Purchase #2	$86.25	7.121%	$92.3919	$92.39	$92.40	$92.40
Purchase #3	$71.66	11.643%	$80.0034	$80.00	$80.00	$80.00
Purchase #4	$18.27	13.487%	$20.7341	$20.73	$20.75	$20.70
Purchase #5	$56.95	10.208%	$62.7635	$62.76	$62.75	$62.80
Purchase #6	$142.30	11.759%	$159.0331	$159.03	$159.05	$159.00
Purchase #7	$47.54	6.455%	$50.6087	$50.61	$50.60	$50.60
7 purchase totals =	$646.52		$699.9112	$699.90	$699.95	$699.90