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	$37.96	10.823%	$42.0684	$42.07	$42.05	$42.10
Purchase #2	$205.92	4.238%	$214.6469	$214.65	$214.65	$214.60
Purchase #3	$60.26	5.693%	$63.6906	$63.69	$63.70	$63.70
Purchase #4	$83.25	6.798%	$88.9093	$88.91	$88.90	$88.90
Purchase #5	$48.70	6.529%	$51.8796	$51.88	$51.90	$51.90
Purchase #6	$68.26	5.588%	$72.0744	$72.07	$72.05	$72.10
Purchase #7	$128.97	11.844%	$144.2452	$144.25	$144.25	$144.20
7 purchase totals =	$633.32		$677.5144	$677.52	$677.50	$677.50