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	$52.67	12.604%	$59.3085	$59.31	$59.30	$59.30
Purchase #2	$108.79	5.617%	$114.9007	$114.90	$114.90	$114.90
Purchase #3	$214.71	3.793%	$222.854	$222.85	$222.85	$222.90
Purchase #4	$120.88	10.845%	$133.9894	$133.99	$134.00	$134.00
Purchase #5	$88.86	6.360%	$94.5115	$94.51	$94.50	$94.50
Purchase #6	$64.37	9.504%	$70.4877	$70.49	$70.50	$70.50
Purchase #7	$57.49	13.261%	$65.1137	$65.11	$65.10	$65.10
7 purchase totals =	$707.77		$761.1655	$761.16	$761.15	$761.20