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	$50.35	5.493%	$53.1157	$53.12	$53.10	$53.10
Purchase #2	$50.70	8.750%	$55.1363	$55.14	$55.15	$55.10
Purchase #3	$142.76	3.700%	$148.0421	$148.04	$148.05	$148.00
Purchase #4	$56.86	4.788%	$59.5825	$59.58	$59.60	$59.60
Purchase #5	$167.90	6.327%	$178.523	$178.52	$178.50	$178.50
Purchase #6	$49.91	12.410%	$56.1038	$56.10	$56.10	$56.10
Purchase #7	$90.30	3.145%	$93.1399	$93.14	$93.15	$93.10
7 purchase totals =	$608.78		$643.6433	$643.64	$643.65	$643.50