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	$137.37	11.602%	$153.3077	$153.31	$153.30	$153.30
Purchase #2	$78.79	13.822%	$89.6804	$89.68	$89.70	$89.70
Purchase #3	$165.93	4.441%	$173.299	$173.30	$173.30	$173.30
Purchase #4	$45.41	11.120%	$50.4596	$50.46	$50.45	$50.50
Purchase #5	$165.39	13.579%	$187.8483	$187.85	$187.85	$187.80
Purchase #6	$75.26	11.324%	$83.7824	$83.78	$83.80	$83.80
Purchase #7	$85.46	7.149%	$91.5695	$91.57	$91.55	$91.60
7 purchase totals =	$753.61		$829.9469	$829.95	$829.95	$830.00