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	$50.40	13.160%	$57.0326	$57.03	$57.05	$57.00
Purchase #2	$61.56	10.603%	$68.0872	$68.09	$68.10	$68.10
Purchase #3	$37.86	11.210%	$42.1041	$42.10	$42.10	$42.10
Purchase #4	$57.64	8.449%	$62.51	$62.51	$62.50	$62.50
Purchase #5	$90.36	5.466%	$95.2991	$95.30	$95.30	$95.30
Purchase #6	$9.71	12.865%	$10.9592	$10.96	$10.95	$11.00
Purchase #7	$187.71	4.617%	$196.3766	$196.38	$196.40	$196.40
7 purchase totals =	$495.24		$532.3688	$532.37	$532.40	$532.40