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	$10.76	3.705%	$11.1587	$11.16	$11.15	$11.20
Purchase #2	$40.53	3.205%	$41.829	$41.83	$41.85	$41.80
Purchase #3	$207.76	10.343%	$229.2486	$229.25	$229.25	$229.20
Purchase #4	$248.72	9.421%	$272.1519	$272.15	$272.15	$272.20
Purchase #5	$221.38	5.390%	$233.3124	$233.31	$233.30	$233.30
Purchase #6	$40.28	8.265%	$43.6091	$43.61	$43.60	$43.60
Purchase #7	$76.44	11.851%	$85.4989	$85.50	$85.50	$85.50
7 purchase totals =	$845.87		$916.8086	$916.81	$916.80	$916.80