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	$184.43	12.391%	$207.2827	$207.28	$207.30	$207.30
Purchase #2	$136.77	6.389%	$145.5082	$145.51	$145.50	$145.50
Purchase #3	$243.54	6.512%	$259.3993	$259.40	$259.40	$259.40
Purchase #4	$149.43	12.737%	$168.4629	$168.46	$168.45	$168.50
Purchase #5	$141.60	9.769%	$155.4329	$155.43	$155.45	$155.40
Purchase #6	$9.64	13.137%	$10.9064	$10.91	$10.90	$10.90
Purchase #7	$47.90	12.321%	$53.8018	$53.80	$53.80	$53.80
7 purchase totals =	$913.31		$1,000.7942	$1,000.79	$1,000.80	$1,000.80