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	$44.31	3.416%	$45.8236	$45.82	$45.80	$45.80
Purchase #2	$142.40	5.839%	$150.7147	$150.71	$150.70	$150.70
Purchase #3	$25.70	7.319%	$27.581	$27.58	$27.60	$27.60
Purchase #4	$10.68	11.163%	$11.8722	$11.87	$11.85	$11.90
Purchase #5	$102.51	6.468%	$109.1403	$109.14	$109.15	$109.10
Purchase #6	$236.50	8.603%	$256.8461	$256.85	$256.85	$256.80
Purchase #7	$58.74	3.699%	$60.9128	$60.91	$60.90	$60.90
7 purchase totals =	$620.84		$662.8907	$662.88	$662.85	$662.80