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	$65.34	7.394%	$70.1712	$70.17	$70.15	$70.20
Purchase #2	$51.67	10.327%	$57.006	$57.01	$57.00	$57.00
Purchase #3	$85.85	5.708%	$90.7503	$90.75	$90.75	$90.80
Purchase #4	$175.85	10.599%	$194.4883	$194.49	$194.50	$194.50
Purchase #5	$63.40	4.618%	$66.3278	$66.33	$66.35	$66.30
Purchase #6	$63.90	12.761%	$72.0543	$72.05	$72.05	$72.10
Purchase #7	$218.60	12.858%	$246.7076	$246.71	$246.70	$246.70
7 purchase totals =	$724.61		$797.5055	$797.51	$797.50	$797.60