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	$11.95	4.657%	$12.5065	$12.51	$12.50	$12.50
Purchase #2	$39.29	11.739%	$43.9023	$43.90	$43.90	$43.90
Purchase #3	$74.51	10.106%	$82.04	$82.04	$82.05	$82.00
Purchase #4	$212.94	7.642%	$229.2129	$229.21	$229.20	$229.20
Purchase #5	$115.29	10.275%	$127.136	$127.14	$127.15	$127.10
Purchase #6	$159.70	12.855%	$180.2294	$180.23	$180.25	$180.20
Purchase #7	$17.83	4.444%	$18.6224	$18.62	$18.60	$18.60
7 purchase totals =	$631.51		$693.6495	$693.65	$693.65	$693.50