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	$28.94	4.476%	$30.2354	$30.24	$30.25	$30.20
Purchase #2	$154.78	6.792%	$165.2927	$165.29	$165.30	$165.30
Purchase #3	$203.70	4.360%	$212.5813	$212.58	$212.60	$212.60
Purchase #4	$46.93	11.834%	$52.4837	$52.48	$52.50	$52.50
Purchase #5	$142.31	3.108%	$146.733	$146.73	$146.75	$146.70
Purchase #6	$147.71	7.380%	$158.611	$158.61	$158.60	$158.60
Purchase #7	$14.53	7.155%	$15.5696	$15.57	$15.55	$15.60
7 purchase totals =	$738.90		$781.5067	$781.50	$781.55	$781.50