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	$90.26	11.692%	$100.8132	$100.81	$100.80	$100.80
Purchase #2	$178.77	3.679%	$185.3469	$185.35	$185.35	$185.30
Purchase #3	$119.92	6.562%	$127.7892	$127.79	$127.80	$127.80
Purchase #4	$48.91	3.485%	$50.6145	$50.61	$50.60	$50.60
Purchase #5	$226.48	9.564%	$248.1405	$248.14	$248.15	$248.10
Purchase #6	$51.91	3.123%	$53.5311	$53.53	$53.55	$53.50
Purchase #7	$230.45	5.450%	$243.0095	$243.01	$243.00	$243.00
7 purchase totals =	$946.70		$1,009.2449	$1,009.24	$1,009.25	$1,009.10