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	$156.74	10.302%	$172.8874	$172.89	$172.90	$172.90
Purchase #2	$55.59	9.381%	$60.8049	$60.80	$60.80	$60.80
Purchase #3	$237.87	6.747%	$253.9191	$253.92	$253.90	$253.90
Purchase #4	$65.61	9.165%	$71.6232	$71.62	$71.60	$71.60
Purchase #5	$6.74	3.805%	$6.9965	$7.00	$7.00	$7.00
Purchase #6	$12.57	12.630%	$14.1576	$14.16	$14.15	$14.20
Purchase #7	$223.50	12.524%	$251.4911	$251.49	$251.50	$251.50
7 purchase totals =	$758.62		$831.8798	$831.88	$831.85	$831.90