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	$26.90	5.804%	$28.4613	$28.46	$28.45	$28.50
Purchase #2	$36.73	4.720%	$38.4637	$38.46	$38.45	$38.50
Purchase #3	$69.90	12.191%	$78.4215	$78.42	$78.40	$78.40
Purchase #4	$206.62	12.222%	$231.8731	$231.87	$231.85	$231.90
Purchase #5	$107.79	3.644%	$111.7179	$111.72	$111.70	$111.70
Purchase #6	$69.84	13.501%	$79.2691	$79.27	$79.25	$79.30
Purchase #7	$89.64	11.399%	$99.8581	$99.86	$99.85	$99.90
7 purchase totals =	$607.42		$668.0647	$668.06	$667.95	$668.20