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	$119.29	3.363%	$123.3017	$123.30	$123.30	$123.30
Purchase #2	$170.63	10.553%	$188.6366	$188.64	$188.65	$188.60
Purchase #3	$47.69	5.708%	$50.4121	$50.41	$50.40	$50.40
Purchase #4	$126.75	7.303%	$136.0066	$136.01	$136.00	$136.00
Purchase #5	$84.95	13.566%	$96.4743	$96.47	$96.45	$96.50
Purchase #6	$105.82	6.371%	$112.5618	$112.56	$112.55	$112.60
Purchase #7	$44.58	12.421%	$50.1173	$50.12	$50.10	$50.10
7 purchase totals =	$699.71		$757.5104	$757.51	$757.45	$757.50