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	$132.41	6.725%	$141.3146	$141.31	$141.30	$141.30
Purchase #2	$120.85	9.457%	$132.2788	$132.28	$132.30	$132.30
Purchase #3	$182.84	11.489%	$203.8465	$203.85	$203.85	$203.80
Purchase #4	$207.41	10.850%	$229.914	$229.91	$229.90	$229.90
Purchase #5	$87.72	13.667%	$99.7087	$99.71	$99.70	$99.70
Purchase #6	$40.89	7.418%	$43.9232	$43.92	$43.90	$43.90
Purchase #7	$21.60	3.164%	$22.2834	$22.28	$22.30	$22.30
7 purchase totals =	$793.72		$873.2692	$873.26	$873.25	$873.20