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	$99.82	6.830%	$106.6377	$106.64	$106.65	$106.60
Purchase #2	$38.43	10.695%	$42.5401	$42.54	$42.55	$42.50
Purchase #3	$230.46	12.500%	$259.2675	$259.27	$259.25	$259.30
Purchase #4	$117.39	8.297%	$127.1298	$127.13	$127.15	$127.10
Purchase #5	$144.63	8.390%	$156.7645	$156.76	$156.75	$156.80
Purchase #6	$209.54	13.381%	$237.5785	$237.58	$237.60	$237.60
Purchase #7	$184.85	10.715%	$204.6567	$204.66	$204.65	$204.70
7 purchase totals =	$1,025.12		$1,134.5748	$1,134.58	$1,134.60	$1,134.60