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	$159.57	12.539%	$179.5785	$179.58	$179.60	$179.60
Purchase #2	$131.49	4.665%	$137.624	$137.62	$137.60	$137.60
Purchase #3	$174.47	12.383%	$196.0746	$196.07	$196.05	$196.10
Purchase #4	$187.71	4.743%	$196.6131	$196.61	$196.60	$196.60
Purchase #5	$140.49	4.566%	$146.9048	$146.90	$146.90	$146.90
Purchase #6	$95.45	10.228%	$105.2126	$105.21	$105.20	$105.20
Purchase #7	$162.81	6.843%	$173.9511	$173.95	$173.95	$174.00
7 purchase totals =	$1,051.99		$1,135.9587	$1,135.94	$1,135.90	$1,136.00