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	$105.78	5.661%	$111.7682	$111.77	$111.75	$111.80
Purchase #2	$73.25	13.180%	$82.9044	$82.90	$82.90	$82.90
Purchase #3	$247.72	13.556%	$281.3009	$281.30	$281.30	$281.30
Purchase #4	$176.60	4.356%	$184.2927	$184.29	$184.30	$184.30
Purchase #5	$45.66	7.765%	$49.2055	$49.21	$49.20	$49.20
Purchase #6	$73.31	3.492%	$75.87	$75.87	$75.85	$75.90
Purchase #7	$18.60	13.712%	$21.1504	$21.15	$21.15	$21.20
7 purchase totals =	$740.92		$806.4921	$806.49	$806.45	$806.60