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	$80.25	9.427%	$87.8152	$87.82	$87.80	$87.80
Purchase #2	$155.52	9.541%	$170.3582	$170.36	$170.35	$170.40
Purchase #3	$51.39	5.198%	$54.0613	$54.06	$54.05	$54.10
Purchase #4	$165.84	11.870%	$185.5252	$185.53	$185.55	$185.50
Purchase #5	$12.53	10.388%	$13.8316	$13.83	$13.85	$13.80
Purchase #6	$73.43	13.491%	$83.3364	$83.34	$83.35	$83.30
Purchase #7	$82.29	7.175%	$88.1943	$88.19	$88.20	$88.20
7 purchase totals =	$621.25		$683.1222	$683.13	$683.15	$683.10