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	$37.77	5.229%	$39.745	$39.75	$39.75	$39.70
Purchase #2	$154.32	12.262%	$173.2427	$173.24	$173.25	$173.20
Purchase #3	$241.79	11.208%	$268.8898	$268.89	$268.90	$268.90
Purchase #4	$87.95	13.422%	$99.7546	$99.75	$99.75	$99.80
Purchase #5	$195.31	9.450%	$213.7668	$213.77	$213.75	$213.80
Purchase #6	$66.83	9.655%	$73.2824	$73.28	$73.30	$73.30
Purchase #7	$91.51	9.167%	$99.8987	$99.90	$99.90	$99.90
7 purchase totals =	$875.48		$968.5800	$968.58	$968.60	$968.60