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	$11.46	6.650%	$12.2221	$12.22	$12.20	$12.20
Purchase #2	$85.58	6.750%	$91.3567	$91.36	$91.35	$91.40
Purchase #3	$228.72	6.704%	$244.0534	$244.05	$244.05	$244.10
Purchase #4	$90.41	10.805%	$100.1788	$100.18	$100.20	$100.20
Purchase #5	$24.43	9.761%	$26.8146	$26.81	$26.80	$26.80
Purchase #6	$63.99	13.188%	$72.429	$72.43	$72.45	$72.40
Purchase #7	$81.48	10.659%	$90.165	$90.17	$90.15	$90.20
7 purchase totals =	$586.07		$637.2196	$637.22	$637.20	$637.30