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	$6.61	10.107%	$7.2781	$7.28	$7.30	$7.30
Purchase #2	$48.66	4.593%	$50.895	$50.90	$50.90	$50.90
Purchase #3	$191.65	7.112%	$205.2801	$205.28	$205.30	$205.30
Purchase #4	$201.85	10.677%	$223.4015	$223.40	$223.40	$223.40
Purchase #5	$246.42	10.595%	$272.5282	$272.53	$272.55	$272.50
Purchase #6	$10.71	13.562%	$12.1625	$12.16	$12.15	$12.20
Purchase #7	$208.76	10.858%	$231.4272	$231.43	$231.45	$231.40
7 purchase totals =	$914.66		$1,002.9726	$1,002.98	$1,003.05	$1,003.00