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	$249.58	6.135%	$264.8917	$264.89	$264.90	$264.90
Purchase #2	$70.84	13.861%	$80.6591	$80.66	$80.65	$80.70
Purchase #3	$80.35	3.187%	$82.9108	$82.91	$82.90	$82.90
Purchase #4	$100.32	8.230%	$108.5763	$108.58	$108.60	$108.60
Purchase #5	$233.48	4.485%	$243.9516	$243.95	$243.95	$244.00
Purchase #6	$27.41	9.160%	$29.9208	$29.92	$29.90	$29.90
Purchase #7	$195.96	13.571%	$222.5537	$222.55	$222.55	$222.60
7 purchase totals =	$957.94		$1,033.4640	$1,033.46	$1,033.45	$1,033.60