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	$146.46	11.676%	$163.5607	$163.56	$163.55	$163.60
Purchase #2	$50.44	3.229%	$52.0687	$52.07	$52.05	$52.10
Purchase #3	$170.43	8.268%	$184.5212	$184.52	$184.50	$184.50
Purchase #4	$238.41	6.447%	$253.7803	$253.78	$253.80	$253.80
Purchase #5	$76.28	9.290%	$83.3664	$83.37	$83.35	$83.40
Purchase #6	$72.49	8.337%	$78.5335	$78.53	$78.55	$78.50
Purchase #7	$49.32	10.754%	$54.6239	$54.62	$54.60	$54.60
7 purchase totals =	$803.83		$870.4547	$870.45	$870.40	$870.50