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	$179.27	5.333%	$188.8305	$188.83	$188.85	$188.80
Purchase #2	$210.78	5.866%	$223.1444	$223.14	$223.15	$223.10
Purchase #3	$162.70	6.127%	$172.6686	$172.67	$172.65	$172.70
Purchase #4	$217.96	6.182%	$231.4343	$231.43	$231.45	$231.40
Purchase #5	$41.27	3.640%	$42.7722	$42.77	$42.75	$42.80
Purchase #6	$61.48	10.758%	$68.094	$68.09	$68.10	$68.10
Purchase #7	$43.33	11.253%	$48.2059	$48.21	$48.20	$48.20
7 purchase totals =	$916.79		$975.1499	$975.14	$975.15	$975.10