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	$114.52	3.300%	$118.2992	$118.30	$118.30	$118.30
Purchase #2	$48.78	8.404%	$52.8795	$52.88	$52.90	$52.90
Purchase #3	$211.59	8.648%	$229.8883	$229.89	$229.90	$229.90
Purchase #4	$216.72	7.323%	$232.5904	$232.59	$232.60	$232.60
Purchase #5	$69.51	11.313%	$77.3737	$77.37	$77.35	$77.40
Purchase #6	$178.26	10.285%	$196.594	$196.59	$196.60	$196.60
Purchase #7	$72.66	11.723%	$81.1779	$81.18	$81.20	$81.20
7 purchase totals =	$912.04		$988.8030	$988.80	$988.85	$988.90