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	$118.33	11.150%	$131.5238	$131.52	$131.50	$131.50
Purchase #2	$86.25	4.811%	$90.3995	$90.40	$90.40	$90.40
Purchase #3	$232.38	6.103%	$246.5622	$246.56	$246.55	$246.60
Purchase #4	$221.51	5.248%	$233.1348	$233.13	$233.15	$233.10
Purchase #5	$113.84	7.178%	$122.0114	$122.01	$122.00	$122.00
Purchase #6	$79.36	12.225%	$89.0618	$89.06	$89.05	$89.10
Purchase #7	$199.84	10.604%	$221.031	$221.03	$221.05	$221.00
7 purchase totals =	$1,051.51		$1,133.7245	$1,133.71	$1,133.70	$1,133.70