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	$139.47	3.833%	$144.8159	$144.82	$144.80	$144.80
Purchase #2	$12.34	4.567%	$12.9036	$12.90	$12.90	$12.90
Purchase #3	$210.83	3.555%	$218.325	$218.33	$218.35	$218.30
Purchase #4	$20.98	8.142%	$22.6882	$22.69	$22.70	$22.70
Purchase #5	$158.77	9.148%	$173.2943	$173.29	$173.30	$173.30
Purchase #6	$92.48	7.194%	$99.133	$99.13	$99.15	$99.10
Purchase #7	$211.38	13.222%	$239.3287	$239.33	$239.35	$239.30
7 purchase totals =	$846.25		$910.4887	$910.49	$910.55	$910.40