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	$79.90	13.817%	$90.9398	$90.94	$90.95	$90.90
Purchase #2	$46.58	4.222%	$48.5466	$48.55	$48.55	$48.50
Purchase #3	$72.96	4.246%	$76.0579	$76.06	$76.05	$76.10
Purchase #4	$20.96	6.344%	$22.2897	$22.29	$22.30	$22.30
Purchase #5	$51.52	8.327%	$55.8101	$55.81	$55.80	$55.80
Purchase #6	$102.69	6.187%	$109.0434	$109.04	$109.05	$109.00
Purchase #7	$113.29	3.223%	$116.9413	$116.94	$116.95	$116.90
7 purchase totals =	$487.90		$519.6288	$519.63	$519.65	$519.50