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	$8.89	13.354%	$10.0772	$10.08	$10.10	$10.10
Purchase #2	$91.77	10.546%	$101.4481	$101.45	$101.45	$101.40
Purchase #3	$13.93	7.253%	$14.9403	$14.94	$14.95	$14.90
Purchase #4	$169.81	9.834%	$186.5091	$186.51	$186.50	$186.50
Purchase #5	$192.68	9.103%	$210.2197	$210.22	$210.20	$210.20
Purchase #6	$183.34	11.691%	$204.7743	$204.77	$204.75	$204.80
Purchase #7	$222.54	12.727%	$250.8627	$250.86	$250.85	$250.90
7 purchase totals =	$882.96		$978.8314	$978.83	$978.80	$978.80