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	$211.87	4.205%	$220.7791	$220.78	$220.80	$220.80
Purchase #2	$144.33	6.160%	$153.2207	$153.22	$153.20	$153.20
Purchase #3	$134.68	12.352%	$151.3157	$151.32	$151.30	$151.30
Purchase #4	$145.38	7.489%	$156.2675	$156.27	$156.25	$156.30
Purchase #5	$162.96	10.742%	$180.4652	$180.47	$180.45	$180.50
Purchase #6	$215.56	13.390%	$244.4235	$244.42	$244.40	$244.40
Purchase #7	$228.82	12.273%	$256.9031	$256.90	$256.90	$256.90
7 purchase totals =	$1,243.60		$1,363.3748	$1,363.38	$1,363.30	$1,363.40