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	$32.46	3.121%	$33.4731	$33.47	$33.45	$33.50
Purchase #2	$100.77	11.325%	$112.1822	$112.18	$112.20	$112.20
Purchase #3	$145.43	9.747%	$159.6051	$159.61	$159.60	$159.60
Purchase #4	$44.78	4.373%	$46.7382	$46.74	$46.75	$46.70
Purchase #5	$35.68	4.683%	$37.3509	$37.35	$37.35	$37.40
Purchase #6	$48.91	8.703%	$53.1666	$53.17	$53.15	$53.20
Purchase #7	$208.73	3.740%	$216.5365	$216.54	$216.55	$216.50
7 purchase totals =	$616.76		$659.0526	$659.06	$659.05	$659.10