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	$88.74	12.589%	$99.9115	$99.91	$99.90	$99.90
Purchase #2	$160.26	5.198%	$168.5903	$168.59	$168.60	$168.60
Purchase #3	$29.27	12.211%	$32.8442	$32.84	$32.85	$32.80
Purchase #4	$208.94	7.263%	$224.1153	$224.12	$224.10	$224.10
Purchase #5	$64.86	4.591%	$67.8377	$67.84	$67.85	$67.80
Purchase #6	$67.48	3.400%	$69.7743	$69.77	$69.75	$69.80
Purchase #7	$139.72	10.494%	$154.3822	$154.38	$154.40	$154.40
7 purchase totals =	$759.27		$817.4555	$817.45	$817.45	$817.40