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	$84.83	5.832%	$89.7773	$89.78	$89.80	$89.80
Purchase #2	$173.48	7.440%	$186.3869	$186.39	$186.40	$186.40
Purchase #3	$85.45	5.750%	$90.3634	$90.36	$90.35	$90.40
Purchase #4	$82.50	11.620%	$92.0865	$92.09	$92.10	$92.10
Purchase #5	$10.64	10.181%	$11.7233	$11.72	$11.70	$11.70
Purchase #6	$53.72	7.775%	$57.8967	$57.90	$57.90	$57.90
Purchase #7	$22.64	3.205%	$23.3656	$23.37	$23.35	$23.40
7 purchase totals =	$513.26		$551.5997	$551.61	$551.60	$551.70