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	$14.72	9.550%	$16.1258	$16.13	$16.15	$16.10
Purchase #2	$91.53	9.788%	$100.489	$100.49	$100.50	$100.50
Purchase #3	$163.47	13.244%	$185.12	$185.12	$185.10	$185.10
Purchase #4	$85.55	9.195%	$93.4163	$93.42	$93.40	$93.40
Purchase #5	$103.36	7.440%	$111.05	$111.05	$111.05	$111.10
Purchase #6	$10.51	7.739%	$11.3234	$11.32	$11.30	$11.30
Purchase #7	$36.34	5.839%	$38.4619	$38.46	$38.45	$38.50
7 purchase totals =	$505.48		$555.9864	$555.99	$555.95	$556.00