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	$79.69	13.657%	$90.5733	$90.57	$90.55	$90.60
Purchase #2	$54.94	8.355%	$59.5302	$59.53	$59.55	$59.50
Purchase #3	$20.90	3.636%	$21.6599	$21.66	$21.65	$21.70
Purchase #4	$19.90	6.458%	$21.1851	$21.19	$21.20	$21.20
Purchase #5	$87.78	7.103%	$94.015	$94.02	$94.00	$94.00
Purchase #6	$49.33	3.651%	$51.131	$51.13	$51.15	$51.10
Purchase #7	$171.49	7.338%	$184.0739	$184.07	$184.05	$184.10
7 purchase totals =	$484.03		$522.1684	$522.17	$522.15	$522.20