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	$131.46	9.773%	$144.3076	$144.31	$144.30	$144.30
Purchase #2	$156.56	9.496%	$171.4269	$171.43	$171.45	$171.40
Purchase #3	$49.37	13.724%	$56.1455	$56.15	$56.15	$56.10
Purchase #4	$58.51	11.277%	$65.1082	$65.11	$65.10	$65.10
Purchase #5	$244.86	13.457%	$277.8108	$277.81	$277.80	$277.80
Purchase #6	$198.92	7.587%	$214.0121	$214.01	$214.00	$214.00
Purchase #7	$50.61	13.118%	$57.249	$57.25	$57.25	$57.20
7 purchase totals =	$890.29		$986.0601	$986.07	$986.05	$985.90