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	$245.31	10.375%	$270.7609	$270.76	$270.75	$270.80
Purchase #2	$14.72	6.389%	$15.6605	$15.66	$15.65	$15.70
Purchase #3	$71.42	9.395%	$78.1299	$78.13	$78.15	$78.10
Purchase #4	$208.27	12.482%	$234.2663	$234.27	$234.25	$234.30
Purchase #5	$50.94	12.400%	$57.2566	$57.26	$57.25	$57.30
Purchase #6	$60.45	10.409%	$66.7422	$66.74	$66.75	$66.70
Purchase #7	$193.90	13.253%	$219.5976	$219.60	$219.60	$219.60
7 purchase totals =	$845.01		$942.4140	$942.42	$942.40	$942.50