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	$150.76	6.665%	$160.8082	$160.81	$160.80	$160.80
Purchase #2	$133.47	5.855%	$141.2847	$141.28	$141.30	$141.30
Purchase #3	$37.53	4.315%	$39.1494	$39.15	$39.15	$39.10
Purchase #4	$87.70	9.144%	$95.7193	$95.72	$95.70	$95.70
Purchase #5	$105.25	13.293%	$119.2409	$119.24	$119.25	$119.20
Purchase #6	$37.46	11.834%	$41.893	$41.89	$41.90	$41.90
Purchase #7	$11.42	10.428%	$12.6109	$12.61	$12.60	$12.60
7 purchase totals =	$563.59		$610.7064	$610.70	$610.70	$610.60