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	$43.61	5.301%	$45.9218	$45.92	$45.90	$45.90
Purchase #2	$225.76	7.465%	$242.613	$242.61	$242.60	$242.60
Purchase #3	$134.58	8.832%	$146.4661	$146.47	$146.45	$146.50
Purchase #4	$207.65	6.847%	$221.8678	$221.87	$221.85	$221.90
Purchase #5	$39.37	3.424%	$40.718	$40.72	$40.70	$40.70
Purchase #6	$127.94	5.177%	$134.5635	$134.56	$134.55	$134.60
Purchase #7	$147.60	7.726%	$159.0036	$159.00	$159.00	$159.00
7 purchase totals =	$926.51		$991.1538	$991.15	$991.05	$991.20