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	$50.85	7.184%	$54.5031	$54.50	$54.50	$54.50
Purchase #2	$205.82	13.409%	$233.4184	$233.42	$233.40	$233.40
Purchase #3	$96.26	9.122%	$105.0408	$105.04	$105.05	$105.00
Purchase #4	$99.44	8.785%	$108.1758	$108.18	$108.20	$108.20
Purchase #5	$31.42	3.127%	$32.4025	$32.40	$32.40	$32.40
Purchase #6	$149.62	11.659%	$167.0642	$167.06	$167.05	$167.10
Purchase #7	$112.78	6.408%	$120.0069	$120.01	$120.00	$120.00
7 purchase totals =	$746.19		$820.6117	$820.61	$820.60	$820.60