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	$165.46	11.752%	$184.9049	$184.90	$184.90	$184.90
Purchase #2	$198.26	11.666%	$221.389	$221.39	$221.40	$221.40
Purchase #3	$149.59	11.232%	$166.3919	$166.39	$166.40	$166.40
Purchase #4	$52.63	6.631%	$56.1199	$56.12	$56.10	$56.10
Purchase #5	$134.60	3.871%	$139.8104	$139.81	$139.80	$139.80
Purchase #6	$133.37	13.802%	$151.7777	$151.78	$151.80	$151.80
Purchase #7	$108.97	8.350%	$118.069	$118.07	$118.05	$118.10
7 purchase totals =	$942.88		$1,038.4628	$1,038.46	$1,038.45	$1,038.50