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	$57.57	11.335%	$64.0956	$64.10	$64.10	$64.10
Purchase #2	$132.26	8.475%	$143.469	$143.47	$143.45	$143.50
Purchase #3	$204.90	8.525%	$222.3677	$222.37	$222.35	$222.40
Purchase #4	$60.83	9.586%	$66.6612	$66.66	$66.65	$66.70
Purchase #5	$215.91	10.471%	$238.5179	$238.52	$238.50	$238.50
Purchase #6	$86.53	9.632%	$94.8646	$94.86	$94.85	$94.90
Purchase #7	$14.83	4.117%	$15.4406	$15.44	$15.45	$15.40
7 purchase totals =	$772.83		$845.4166	$845.42	$845.35	$845.50