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	$21.30	3.236%	$21.9893	$21.99	$22.00	$22.00
Purchase #2	$125.63	4.566%	$131.3663	$131.37	$131.35	$131.40
Purchase #3	$145.52	8.696%	$158.1744	$158.17	$158.15	$158.20
Purchase #4	$127.85	13.333%	$144.8962	$144.90	$144.90	$144.90
Purchase #5	$73.28	13.185%	$82.942	$82.94	$82.95	$82.90
Purchase #6	$198.81	11.337%	$221.3491	$221.35	$221.35	$221.30
Purchase #7	$222.67	4.457%	$232.5944	$232.59	$232.60	$232.60
7 purchase totals =	$915.06		$993.3117	$993.31	$993.30	$993.30