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	$30.36	9.519%	$33.25	$33.25	$33.25	$33.30
Purchase #2	$242.36	13.778%	$275.7524	$275.75	$275.75	$275.80
Purchase #3	$225.30	7.259%	$241.6545	$241.65	$241.65	$241.70
Purchase #4	$139.86	13.733%	$159.067	$159.07	$159.05	$159.10
Purchase #5	$15.28	3.666%	$15.8402	$15.84	$15.85	$15.80
Purchase #6	$85.59	4.350%	$89.3132	$89.31	$89.30	$89.30
Purchase #7	$56.89	11.140%	$63.2275	$63.23	$63.25	$63.20
7 purchase totals =	$795.64		$878.1048	$878.10	$878.10	$878.20