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	$143.90	12.296%	$161.5939	$161.59	$161.60	$161.60
Purchase #2	$175.38	12.626%	$197.5235	$197.52	$197.50	$197.50
Purchase #3	$164.97	5.215%	$173.5732	$173.57	$173.55	$173.60
Purchase #4	$123.37	13.161%	$139.6067	$139.61	$139.60	$139.60
Purchase #5	$64.72	8.180%	$70.0141	$70.01	$70.00	$70.00
Purchase #6	$119.61	6.793%	$127.7351	$127.74	$127.75	$127.70
Purchase #7	$171.44	11.341%	$190.883	$190.88	$190.90	$190.90
7 purchase totals =	$963.39		$1,060.9295	$1,060.92	$1,060.90	$1,060.90