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	$47.70	9.859%	$52.4027	$52.40	$52.40	$52.40
Purchase #2	$94.34	6.867%	$100.8183	$100.82	$100.80	$100.80
Purchase #3	$210.27	7.363%	$225.7522	$225.75	$225.75	$225.80
Purchase #4	$137.43	10.257%	$151.5262	$151.53	$151.55	$151.50
Purchase #5	$106.96	10.419%	$118.1042	$118.10	$118.10	$118.10
Purchase #6	$181.70	13.798%	$206.771	$206.77	$206.75	$206.80
Purchase #7	$211.56	5.604%	$223.4158	$223.42	$223.40	$223.40
7 purchase totals =	$989.96		$1,078.7904	$1,078.79	$1,078.75	$1,078.80