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	$101.33	11.743%	$113.2292	$113.23	$113.25	$113.20
Purchase #2	$169.27	8.862%	$184.2707	$184.27	$184.25	$184.30
Purchase #3	$159.47	7.713%	$171.7699	$171.77	$171.75	$171.80
Purchase #4	$36.84	10.822%	$40.8268	$40.83	$40.85	$40.80
Purchase #5	$51.68	8.674%	$56.1627	$56.16	$56.15	$56.20
Purchase #6	$9.51	10.413%	$10.5003	$10.50	$10.50	$10.50
Purchase #7	$195.46	13.667%	$222.1735	$222.17	$222.15	$222.20
7 purchase totals =	$723.56		$798.9331	$798.93	$798.90	$799.00