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	$208.97	6.422%	$222.3901	$222.39	$222.40	$222.40
Purchase #2	$46.72	13.152%	$52.8646	$52.86	$52.85	$52.90
Purchase #3	$85.75	4.250%	$89.3944	$89.39	$89.40	$89.40
Purchase #4	$238.77	12.857%	$269.4687	$269.47	$269.45	$269.50
Purchase #5	$178.43	6.281%	$189.6372	$189.64	$189.65	$189.60
Purchase #6	$222.97	11.748%	$249.1645	$249.16	$249.15	$249.20
Purchase #7	$52.61	5.723%	$55.6209	$55.62	$55.60	$55.60
7 purchase totals =	$1,034.22		$1,128.5404	$1,128.53	$1,128.50	$1,128.60