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	$236.26	4.347%	$246.5302	$246.53	$246.55	$246.50
Purchase #2	$179.27	11.772%	$200.3737	$200.37	$200.35	$200.40
Purchase #3	$137.96	12.702%	$155.4837	$155.48	$155.50	$155.50
Purchase #4	$140.34	6.625%	$149.6375	$149.64	$149.65	$149.60
Purchase #5	$222.48	3.678%	$230.6628	$230.66	$230.65	$230.70
Purchase #6	$49.30	8.374%	$53.4284	$53.43	$53.45	$53.40
Purchase #7	$107.31	3.716%	$111.2976	$111.30	$111.30	$111.30
7 purchase totals =	$1,072.92		$1,147.4139	$1,147.41	$1,147.45	$1,147.40