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	$103.36	7.828%	$111.451	$111.45	$111.45	$111.50
Purchase #2	$139.26	8.148%	$150.6069	$150.61	$150.60	$150.60
Purchase #3	$141.73	12.359%	$159.2464	$159.25	$159.25	$159.20
Purchase #4	$105.56	8.327%	$114.35	$114.35	$114.35	$114.40
Purchase #5	$154.75	3.445%	$160.0811	$160.08	$160.10	$160.10
Purchase #6	$88.49	3.478%	$91.5677	$91.57	$91.55	$91.60
Purchase #7	$19.50	4.482%	$20.374	$20.37	$20.35	$20.40
7 purchase totals =	$752.65		$807.6771	$807.68	$807.65	$807.80