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	$138.42	5.838%	$146.501	$146.50	$146.50	$146.50
Purchase #2	$249.63	11.134%	$277.4238	$277.42	$277.40	$277.40
Purchase #3	$50.53	11.482%	$56.3319	$56.33	$56.35	$56.30
Purchase #4	$139.52	3.430%	$144.3055	$144.31	$144.30	$144.30
Purchase #5	$244.80	4.519%	$255.8625	$255.86	$255.85	$255.90
Purchase #6	$230.47	12.147%	$258.4652	$258.47	$258.45	$258.50
Purchase #7	$93.94	11.247%	$104.5054	$104.51	$104.50	$104.50
7 purchase totals =	$1,147.31		$1,243.3953	$1,243.40	$1,243.35	$1,243.40