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	$45.58	11.384%	$50.7688	$50.77	$50.75	$50.80
Purchase #2	$176.27	5.299%	$185.6105	$185.61	$185.60	$185.60
Purchase #3	$125.95	13.739%	$143.2543	$143.25	$143.25	$143.30
Purchase #4	$122.92	9.585%	$134.7019	$134.70	$134.70	$134.70
Purchase #5	$218.38	11.228%	$242.8997	$242.90	$242.90	$242.90
Purchase #6	$140.64	5.233%	$147.9997	$148.00	$148.00	$148.00
Purchase #7	$167.74	4.641%	$175.5248	$175.52	$175.50	$175.50
7 purchase totals =	$997.48		$1,080.7597	$1,080.75	$1,080.70	$1,080.80