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	$151.78	12.712%	$171.0743	$171.07	$171.05	$171.10
Purchase #2	$158.38	7.663%	$170.5167	$170.52	$170.50	$170.50
Purchase #3	$18.98	11.250%	$21.1153	$21.12	$21.10	$21.10
Purchase #4	$233.64	11.394%	$260.2609	$260.26	$260.25	$260.30
Purchase #5	$155.55	10.764%	$172.2934	$172.29	$172.30	$172.30
Purchase #6	$44.74	13.506%	$50.7826	$50.78	$50.80	$50.80
Purchase #7	$27.85	11.314%	$31.0009	$31.00	$31.00	$31.00
7 purchase totals =	$790.92		$877.0441	$877.04	$877.00	$877.10