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	$170.47	3.182%	$175.8944	$175.89	$175.90	$175.90
Purchase #2	$129.69	12.184%	$145.4914	$145.49	$145.50	$145.50
Purchase #3	$194.73	8.772%	$211.8117	$211.81	$211.80	$211.80
Purchase #4	$175.81	8.249%	$190.3126	$190.31	$190.30	$190.30
Purchase #5	$134.88	3.312%	$139.3472	$139.35	$139.35	$139.30
Purchase #6	$18.83	9.351%	$20.5908	$20.59	$20.60	$20.60
Purchase #7	$63.45	7.115%	$67.9645	$67.96	$67.95	$68.00
7 purchase totals =	$887.86		$951.4126	$951.40	$951.40	$951.40