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	$37.82	13.279%	$42.8421	$42.84	$42.85	$42.80
Purchase #2	$159.49	8.190%	$172.5522	$172.55	$172.55	$172.60
Purchase #3	$34.93	10.624%	$38.641	$38.64	$38.65	$38.60
Purchase #4	$73.31	12.818%	$82.7069	$82.71	$82.70	$82.70
Purchase #5	$27.30	7.220%	$29.2711	$29.27	$29.25	$29.30
Purchase #6	$161.51	11.833%	$180.6215	$180.62	$180.60	$180.60
Purchase #7	$53.91	3.270%	$55.6729	$55.67	$55.65	$55.70
7 purchase totals =	$548.27		$602.3077	$602.30	$602.25	$602.30