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	$97.46	10.324%	$107.5218	$107.52	$107.50	$107.50
Purchase #2	$39.90	5.569%	$42.122	$42.12	$42.10	$42.10
Purchase #3	$208.35	11.165%	$231.6123	$231.61	$231.60	$231.60
Purchase #4	$77.91	6.335%	$82.8456	$82.85	$82.85	$82.80
Purchase #5	$17.34	4.612%	$18.1397	$18.14	$18.15	$18.10
Purchase #6	$157.90	8.303%	$171.0104	$171.01	$171.00	$171.00
Purchase #7	$29.51	13.365%	$33.454	$33.45	$33.45	$33.50
7 purchase totals =	$628.37		$686.7058	$686.70	$686.65	$686.60