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	$9.34	8.590%	$10.1423	$10.14	$10.15	$10.10
Purchase #2	$78.73	4.775%	$82.4894	$82.49	$82.50	$82.50
Purchase #3	$174.95	5.502%	$184.5757	$184.58	$184.60	$184.60
Purchase #4	$143.95	10.781%	$159.4692	$159.47	$159.45	$159.50
Purchase #5	$69.71	11.387%	$77.6479	$77.65	$77.65	$77.60
Purchase #6	$13.99	11.627%	$15.6166	$15.62	$15.60	$15.60
Purchase #7	$30.55	3.312%	$31.5618	$31.56	$31.55	$31.60
7 purchase totals =	$521.22		$561.5029	$561.51	$561.50	$561.50