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	$106.96	12.502%	$120.3321	$120.33	$120.35	$120.30
Purchase #2	$233.31	4.233%	$243.186	$243.19	$243.20	$243.20
Purchase #3	$65.28	11.569%	$72.8322	$72.83	$72.85	$72.80
Purchase #4	$239.67	13.770%	$272.6726	$272.67	$272.65	$272.70
Purchase #5	$20.40	10.817%	$22.6067	$22.61	$22.60	$22.60
Purchase #6	$198.42	3.773%	$205.9064	$205.91	$205.90	$205.90
Purchase #7	$145.28	9.663%	$159.3184	$159.32	$159.30	$159.30
7 purchase totals =	$1,009.32		$1,096.8544	$1,096.86	$1,096.85	$1,096.80