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	$99.74	9.787%	$109.5016	$109.50	$109.50	$109.50
Purchase #2	$47.76	5.831%	$50.5449	$50.54	$50.55	$50.50
Purchase #3	$215.84	13.168%	$244.2618	$244.26	$244.25	$244.30
Purchase #4	$178.82	9.631%	$196.0422	$196.04	$196.05	$196.00
Purchase #5	$242.89	3.498%	$251.3863	$251.39	$251.40	$251.40
Purchase #6	$45.93	4.663%	$48.0717	$48.07	$48.05	$48.10
Purchase #7	$13.85	11.603%	$15.457	$15.46	$15.45	$15.50
7 purchase totals =	$844.83		$915.2655	$915.26	$915.25	$915.30