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	$12.78	3.438%	$13.2194	$13.22	$13.20	$13.20
Purchase #2	$186.77	4.346%	$194.887	$194.89	$194.90	$194.90
Purchase #3	$98.64	6.333%	$104.8869	$104.89	$104.90	$104.90
Purchase #4	$121.95	12.239%	$136.8755	$136.88	$136.90	$136.90
Purchase #5	$167.36	4.261%	$174.4912	$174.49	$174.50	$174.50
Purchase #6	$95.68	8.265%	$103.588	$103.59	$103.60	$103.60
Purchase #7	$190.81	10.526%	$210.8947	$210.89	$210.90	$210.90
7 purchase totals =	$873.99		$938.8427	$938.85	$938.90	$938.90