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	$157.90	9.749%	$173.2937	$173.29	$173.30	$173.30
Purchase #2	$34.46	3.640%	$35.7143	$35.71	$35.70	$35.70
Purchase #3	$159.80	7.832%	$172.3155	$172.32	$172.30	$172.30
Purchase #4	$138.54	9.492%	$151.6902	$151.69	$151.70	$151.70
Purchase #5	$87.93	3.371%	$90.8941	$90.89	$90.90	$90.90
Purchase #6	$63.81	9.376%	$69.7928	$69.79	$69.80	$69.80
Purchase #7	$204.60	11.400%	$227.9244	$227.92	$227.90	$227.90
7 purchase totals =	$847.04		$921.6250	$921.61	$921.60	$921.60