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	$32.80	3.307%	$33.8847	$33.88	$33.90	$33.90
Purchase #2	$174.56	6.868%	$186.5488	$186.55	$186.55	$186.50
Purchase #3	$10.66	4.147%	$11.1021	$11.10	$11.10	$11.10
Purchase #4	$89.92	5.369%	$94.7478	$94.75	$94.75	$94.70
Purchase #5	$81.34	11.692%	$90.8503	$90.85	$90.85	$90.90
Purchase #6	$92.67	13.549%	$105.2259	$105.23	$105.25	$105.20
Purchase #7	$27.77	10.554%	$30.7008	$30.70	$30.70	$30.70
7 purchase totals =	$509.72		$553.0604	$553.06	$553.10	$553.00