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	$17.63	13.686%	$20.0428	$20.04	$20.05	$20.00
Purchase #2	$48.42	10.478%	$53.4934	$53.49	$53.50	$53.50
Purchase #3	$218.56	13.555%	$248.1858	$248.19	$248.20	$248.20
Purchase #4	$64.32	13.722%	$73.146	$73.15	$73.15	$73.10
Purchase #5	$170.41	5.370%	$179.561	$179.56	$179.55	$179.60
Purchase #6	$78.94	12.132%	$88.517	$88.52	$88.50	$88.50
Purchase #7	$51.76	11.606%	$57.7673	$57.77	$57.75	$57.80
7 purchase totals =	$650.04		$720.7133	$720.72	$720.70	$720.70