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	$120.97	13.446%	$137.2356	$137.24	$137.25	$137.20
Purchase #2	$205.55	11.523%	$229.2355	$229.24	$229.25	$229.20
Purchase #3	$238.94	6.634%	$254.7913	$254.79	$254.80	$254.80
Purchase #4	$110.93	7.134%	$118.8437	$118.84	$118.85	$118.80
Purchase #5	$218.36	6.778%	$233.1604	$233.16	$233.15	$233.20
Purchase #6	$87.73	3.582%	$90.8725	$90.87	$90.85	$90.90
Purchase #7	$39.45	8.453%	$42.7847	$42.78	$42.80	$42.80
7 purchase totals =	$1,021.93		$1,106.9237	$1,106.92	$1,106.95	$1,106.90