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	$42.27	7.132%	$45.2847	$45.28	$45.30	$45.30
Purchase #2	$53.93	13.195%	$61.0461	$61.05	$61.05	$61.00
Purchase #3	$177.37	4.390%	$185.1565	$185.16	$185.15	$185.20
Purchase #4	$108.69	4.465%	$113.543	$113.54	$113.55	$113.50
Purchase #5	$230.43	10.329%	$254.2311	$254.23	$254.25	$254.20
Purchase #6	$81.51	11.116%	$90.5707	$90.57	$90.55	$90.60
Purchase #7	$231.57	4.506%	$242.0045	$242.00	$242.00	$242.00
7 purchase totals =	$925.77		$991.8366	$991.83	$991.85	$991.80