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	$46.51	12.136%	$52.1545	$52.15	$52.15	$52.20
Purchase #2	$213.79	12.262%	$240.0049	$240.00	$240.00	$240.00
Purchase #3	$87.94	9.663%	$96.4376	$96.44	$96.45	$96.40
Purchase #4	$54.27	9.476%	$59.4126	$59.41	$59.40	$59.40
Purchase #5	$79.36	7.335%	$85.1811	$85.18	$85.20	$85.20
Purchase #6	$180.69	3.680%	$187.3394	$187.34	$187.35	$187.30
Purchase #7	$32.81	9.185%	$35.8236	$35.82	$35.80	$35.80
7 purchase totals =	$695.37		$756.3537	$756.34	$756.35	$756.30