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	$215.76	3.781%	$223.9179	$223.92	$223.90	$223.90
Purchase #2	$250.96	3.782%	$260.4513	$260.45	$260.45	$260.50
Purchase #3	$150.79	12.511%	$169.6553	$169.66	$169.65	$169.70
Purchase #4	$67.46	12.569%	$75.939	$75.94	$75.95	$75.90
Purchase #5	$163.93	7.353%	$175.9838	$175.98	$176.00	$176.00
Purchase #6	$137.60	4.450%	$143.7232	$143.72	$143.70	$143.70
Purchase #7	$70.34	11.198%	$78.2167	$78.22	$78.20	$78.20
7 purchase totals =	$1,056.84		$1,127.8872	$1,127.89	$1,127.85	$1,127.90