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	$47.92	13.329%	$54.3073	$54.31	$54.30	$54.30
Purchase #2	$177.48	4.107%	$184.7691	$184.77	$184.75	$184.80
Purchase #3	$48.39	12.742%	$54.5559	$54.56	$54.55	$54.60
Purchase #4	$100.64	12.222%	$112.9402	$112.94	$112.95	$112.90
Purchase #5	$20.34	8.530%	$22.075	$22.08	$22.10	$22.10
Purchase #6	$93.66	7.416%	$100.6058	$100.61	$100.60	$100.60
Purchase #7	$129.62	5.817%	$137.16	$137.16	$137.15	$137.20
7 purchase totals =	$618.05		$666.4133	$666.43	$666.40	$666.50