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	$150.50	5.104%	$158.1815	$158.18	$158.20	$158.20
Purchase #2	$100.96	8.599%	$109.6416	$109.64	$109.65	$109.60
Purchase #3	$169.53	12.225%	$190.255	$190.26	$190.25	$190.30
Purchase #4	$48.37	3.680%	$50.15	$50.15	$50.15	$50.20
Purchase #5	$129.84	8.394%	$140.7388	$140.74	$140.75	$140.70
Purchase #6	$64.72	11.358%	$72.0709	$72.07	$72.05	$72.10
Purchase #7	$171.55	6.441%	$182.5995	$182.60	$182.60	$182.60
7 purchase totals =	$835.47		$903.6373	$903.64	$903.65	$903.70