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	$46.93	13.636%	$53.3294	$53.33	$53.35	$53.30
Purchase #2	$57.55	10.797%	$63.7637	$63.76	$63.75	$63.80
Purchase #3	$33.42	11.269%	$37.1861	$37.19	$37.20	$37.20
Purchase #4	$82.37	3.309%	$85.0956	$85.10	$85.10	$85.10
Purchase #5	$155.44	7.194%	$166.6224	$166.62	$166.60	$166.60
Purchase #6	$121.85	12.298%	$136.8351	$136.84	$136.85	$136.80
Purchase #7	$32.89	8.400%	$35.6528	$35.65	$35.65	$35.70
7 purchase totals =	$530.45		$578.4851	$578.49	$578.50	$578.50