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	$30.61	5.601%	$32.3245	$32.32	$32.30	$32.30
Purchase #2	$110.37	7.514%	$118.6632	$118.66	$118.65	$118.70
Purchase #3	$20.33	10.695%	$22.5043	$22.50	$22.50	$22.50
Purchase #4	$96.47	6.784%	$103.0145	$103.01	$103.00	$103.00
Purchase #5	$132.33	3.700%	$137.2262	$137.23	$137.25	$137.20
Purchase #6	$16.47	8.572%	$17.8818	$17.88	$17.90	$17.90
Purchase #7	$153.39	3.193%	$158.2877	$158.29	$158.30	$158.30
7 purchase totals =	$559.97		$589.9022	$589.89	$589.90	$589.90