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	$75.26	4.560%	$78.6919	$78.69	$78.70	$78.70
Purchase #2	$143.99	11.706%	$160.8455	$160.85	$160.85	$160.80
Purchase #3	$198.56	8.753%	$215.94	$215.94	$215.95	$215.90
Purchase #4	$173.38	9.296%	$189.4974	$189.50	$189.50	$189.50
Purchase #5	$100.42	11.691%	$112.1601	$112.16	$112.15	$112.20
Purchase #6	$28.77	12.132%	$32.2604	$32.26	$32.25	$32.30
Purchase #7	$99.27	10.327%	$109.5216	$109.52	$109.50	$109.50
7 purchase totals =	$819.65		$898.9169	$898.92	$898.90	$898.90