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	$227.46	9.525%	$249.1256	$249.13	$249.15	$249.10
Purchase #2	$29.47	10.594%	$32.5921	$32.59	$32.60	$32.60
Purchase #3	$128.37	9.238%	$140.2288	$140.23	$140.25	$140.20
Purchase #4	$155.59	3.684%	$161.3219	$161.32	$161.30	$161.30
Purchase #5	$43.92	13.403%	$49.8066	$49.81	$49.80	$49.80
Purchase #6	$165.50	12.115%	$185.5503	$185.55	$185.55	$185.60
Purchase #7	$18.49	11.852%	$20.6814	$20.68	$20.70	$20.70
7 purchase totals =	$768.80		$839.3067	$839.31	$839.35	$839.30