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	$241.52	9.438%	$264.3147	$264.31	$264.30	$264.30
Purchase #2	$240.57	3.169%	$248.1937	$248.19	$248.20	$248.20
Purchase #3	$197.33	11.440%	$219.9046	$219.90	$219.90	$219.90
Purchase #4	$143.84	5.569%	$151.8504	$151.85	$151.85	$151.90
Purchase #5	$103.89	4.114%	$108.164	$108.16	$108.15	$108.20
Purchase #6	$200.47	13.613%	$227.76	$227.76	$227.75	$227.80
Purchase #7	$231.85	11.301%	$258.0514	$258.05	$258.05	$258.10
7 purchase totals =	$1,359.47		$1,478.2388	$1,478.22	$1,478.20	$1,478.40