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	$234.26	6.628%	$249.7868	$249.79	$249.80	$249.80
Purchase #2	$99.82	11.684%	$111.483	$111.48	$111.50	$111.50
Purchase #3	$137.71	11.317%	$153.2946	$153.29	$153.30	$153.30
Purchase #4	$87.89	9.238%	$96.0093	$96.01	$96.00	$96.00
Purchase #5	$17.77	5.813%	$18.803	$18.80	$18.80	$18.80
Purchase #6	$26.91	11.110%	$29.8997	$29.90	$29.90	$29.90
Purchase #7	$115.36	10.486%	$127.4566	$127.46	$127.45	$127.50
7 purchase totals =	$719.72		$786.7330	$786.73	$786.75	$786.80