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	$200.52	12.268%	$225.1198	$225.12	$225.10	$225.10
Purchase #2	$159.31	3.721%	$165.2379	$165.24	$165.25	$165.20
Purchase #3	$103.69	11.201%	$115.3043	$115.30	$115.30	$115.30
Purchase #4	$241.86	8.454%	$262.3068	$262.31	$262.30	$262.30
Purchase #5	$35.69	6.103%	$37.8682	$37.87	$37.85	$37.90
Purchase #6	$67.27	6.509%	$71.6486	$71.65	$71.65	$71.60
Purchase #7	$74.36	5.256%	$78.2684	$78.27	$78.25	$78.30
7 purchase totals =	$882.70		$955.7540	$955.76	$955.70	$955.70