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	$121.47	8.229%	$131.4658	$131.47	$131.45	$131.50
Purchase #2	$226.30	11.144%	$251.5189	$251.52	$251.50	$251.50
Purchase #3	$170.26	3.471%	$176.1697	$176.17	$176.15	$176.20
Purchase #4	$115.33	11.113%	$128.1466	$128.15	$128.15	$128.10
Purchase #5	$10.60	13.601%	$12.0417	$12.04	$12.05	$12.00
Purchase #6	$50.56	4.171%	$52.6689	$52.67	$52.65	$52.70
Purchase #7	$226.94	7.720%	$244.4598	$244.46	$244.45	$244.50
7 purchase totals =	$921.46		$996.4714	$996.48	$996.40	$996.50