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	$192.75	13.222%	$218.2354	$218.24	$218.25	$218.20
Purchase #2	$204.74	6.582%	$218.216	$218.22	$218.20	$218.20
Purchase #3	$20.76	4.810%	$21.7586	$21.76	$21.75	$21.80
Purchase #4	$241.62	12.262%	$271.2474	$271.25	$271.25	$271.20
Purchase #5	$20.28	10.191%	$22.3467	$22.35	$22.35	$22.30
Purchase #6	$29.46	13.407%	$33.4097	$33.41	$33.40	$33.40
Purchase #7	$204.61	6.164%	$217.2222	$217.22	$217.20	$217.20
7 purchase totals =	$914.22		$1,002.4360	$1,002.45	$1,002.40	$1,002.30