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	$165.89	13.714%	$188.6402	$188.64	$188.65	$188.60
Purchase #2	$143.49	3.738%	$148.8537	$148.85	$148.85	$148.90
Purchase #3	$175.71	5.150%	$184.7591	$184.76	$184.75	$184.80
Purchase #4	$48.62	3.186%	$50.169	$50.17	$50.15	$50.20
Purchase #5	$22.36	12.300%	$25.1103	$25.11	$25.10	$25.10
Purchase #6	$156.70	6.516%	$166.9106	$166.91	$166.90	$166.90
Purchase #7	$228.36	12.223%	$256.2724	$256.27	$256.25	$256.30
7 purchase totals =	$941.13		$1,020.7153	$1,020.71	$1,020.65	$1,020.80