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	$86.88	5.519%	$91.6749	$91.67	$91.65	$91.70
Purchase #2	$172.25	12.644%	$194.0293	$194.03	$194.05	$194.00
Purchase #3	$86.85	13.456%	$98.5365	$98.54	$98.55	$98.50
Purchase #4	$120.40	5.861%	$127.4566	$127.46	$127.45	$127.50
Purchase #5	$160.71	9.589%	$176.1205	$176.12	$176.10	$176.10
Purchase #6	$221.51	4.648%	$231.8058	$231.81	$231.80	$231.80
Purchase #7	$59.77	9.805%	$65.6304	$65.63	$65.65	$65.60
7 purchase totals =	$908.37		$985.2540	$985.26	$985.25	$985.20