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	$153.42	12.165%	$172.0835	$172.08	$172.10	$172.10
Purchase #2	$78.83	8.229%	$85.3169	$85.32	$85.30	$85.30
Purchase #3	$58.76	9.688%	$64.4527	$64.45	$64.45	$64.50
Purchase #4	$89.77	11.276%	$99.8925	$99.89	$99.90	$99.90
Purchase #5	$145.48	11.123%	$161.6617	$161.66	$161.65	$161.70
Purchase #6	$24.74	13.303%	$28.0312	$28.03	$28.05	$28.00
Purchase #7	$139.82	11.126%	$155.3764	$155.38	$155.40	$155.40
7 purchase totals =	$690.82		$766.8149	$766.81	$766.85	$766.90