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	$83.48	6.490%	$88.8979	$88.90	$88.90	$88.90
Purchase #2	$67.28	7.612%	$72.4014	$72.40	$72.40	$72.40
Purchase #3	$216.26	4.164%	$225.2651	$225.27	$225.25	$225.30
Purchase #4	$244.84	8.348%	$265.2792	$265.28	$265.30	$265.30
Purchase #5	$112.90	12.770%	$127.3173	$127.32	$127.30	$127.30
Purchase #6	$131.89	13.285%	$149.4116	$149.41	$149.40	$149.40
Purchase #7	$192.25	5.305%	$202.4489	$202.45	$202.45	$202.40
7 purchase totals =	$1,048.90		$1,131.0214	$1,131.03	$1,131.00	$1,131.00