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	$118.84	9.778%	$130.4602	$130.46	$130.45	$130.50
Purchase #2	$82.75	11.612%	$92.3589	$92.36	$92.35	$92.40
Purchase #3	$153.60	13.818%	$174.8244	$174.82	$174.80	$174.80
Purchase #4	$153.95	12.783%	$173.6294	$173.63	$173.65	$173.60
Purchase #5	$26.64	10.547%	$29.4497	$29.45	$29.45	$29.40
Purchase #6	$26.80	9.573%	$29.3656	$29.37	$29.35	$29.40
Purchase #7	$31.70	5.680%	$33.5006	$33.50	$33.50	$33.50
7 purchase totals =	$594.28		$663.5888	$663.59	$663.55	$663.60