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	$178.73	3.730%	$185.3966	$185.40	$185.40	$185.40
Purchase #2	$153.77	4.592%	$160.8311	$160.83	$160.85	$160.80
Purchase #3	$54.96	5.728%	$58.1081	$58.11	$58.10	$58.10
Purchase #4	$207.86	12.463%	$233.7656	$233.77	$233.75	$233.80
Purchase #5	$79.33	5.662%	$83.8217	$83.82	$83.80	$83.80
Purchase #6	$249.89	6.267%	$265.5506	$265.55	$265.55	$265.60
Purchase #7	$243.31	6.162%	$258.3028	$258.30	$258.30	$258.30
7 purchase totals =	$1,167.85		$1,245.7765	$1,245.78	$1,245.75	$1,245.80