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	$46.61	12.643%	$52.5029	$52.50	$52.50	$52.50
Purchase #2	$211.45	9.247%	$231.0028	$231.00	$231.00	$231.00
Purchase #3	$58.79	9.496%	$64.3727	$64.37	$64.35	$64.40
Purchase #4	$172.43	6.470%	$183.5862	$183.59	$183.60	$183.60
Purchase #5	$165.65	3.738%	$171.842	$171.84	$171.85	$171.80
Purchase #6	$250.68	9.791%	$275.2241	$275.22	$275.20	$275.20
Purchase #7	$32.96	13.539%	$37.4225	$37.42	$37.40	$37.40
7 purchase totals =	$938.57		$1,015.9532	$1,015.94	$1,015.90	$1,015.90