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	$48.29	8.109%	$52.2058	$52.21	$52.20	$52.20
Purchase #2	$99.35	12.652%	$111.9198	$111.92	$111.90	$111.90
Purchase #3	$232.84	5.127%	$244.7777	$244.78	$244.80	$244.80
Purchase #4	$102.82	3.282%	$106.1946	$106.19	$106.20	$106.20
Purchase #5	$167.67	13.509%	$190.3205	$190.32	$190.30	$190.30
Purchase #6	$61.62	4.684%	$64.5063	$64.51	$64.50	$64.50
Purchase #7	$52.79	7.212%	$56.5972	$56.60	$56.60	$56.60
7 purchase totals =	$765.38		$826.5219	$826.53	$826.50	$826.50