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	$149.90	6.418%	$159.5206	$159.52	$159.50	$159.50
Purchase #2	$110.88	8.157%	$119.9245	$119.92	$119.90	$119.90
Purchase #3	$250.66	4.623%	$262.248	$262.25	$262.25	$262.20
Purchase #4	$82.40	8.477%	$89.385	$89.39	$89.40	$89.40
Purchase #5	$65.56	11.826%	$73.3131	$73.31	$73.30	$73.30
Purchase #6	$109.66	13.483%	$124.4455	$124.45	$124.45	$124.40
Purchase #7	$130.90	7.151%	$140.2607	$140.26	$140.25	$140.30
7 purchase totals =	$899.96		$969.0974	$969.10	$969.05	$969.00