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	$161.36	12.157%	$180.9765	$180.98	$181.00	$181.00
Purchase #2	$77.88	5.688%	$82.3098	$82.31	$82.30	$82.30
Purchase #3	$92.87	4.365%	$96.9238	$96.92	$96.90	$96.90
Purchase #4	$231.74	11.540%	$258.4828	$258.48	$258.50	$258.50
Purchase #5	$21.80	7.262%	$23.3831	$23.38	$23.40	$23.40
Purchase #6	$34.62	3.589%	$35.8625	$35.86	$35.85	$35.90
Purchase #7	$7.46	5.848%	$7.8963	$7.90	$7.90	$7.90
7 purchase totals =	$627.73		$685.8348	$685.83	$685.85	$685.90