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	$226.53	13.619%	$257.3811	$257.38	$257.40	$257.40
Purchase #2	$136.74	9.278%	$149.4267	$149.43	$149.45	$149.40
Purchase #3	$129.78	9.717%	$142.3907	$142.39	$142.40	$142.40
Purchase #4	$125.26	11.130%	$139.2014	$139.20	$139.20	$139.20
Purchase #5	$230.89	10.264%	$254.5885	$254.59	$254.60	$254.60
Purchase #6	$106.36	10.308%	$117.3236	$117.32	$117.30	$117.30
Purchase #7	$99.98	11.645%	$111.6227	$111.62	$111.60	$111.60
7 purchase totals =	$1,055.54		$1,171.9347	$1,171.93	$1,171.95	$1,171.90