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	$77.70	7.291%	$83.3651	$83.37	$83.35	$83.40
Purchase #2	$248.56	10.874%	$275.5884	$275.59	$275.60	$275.60
Purchase #3	$216.59	3.874%	$224.9807	$224.98	$225.00	$225.00
Purchase #4	$164.48	13.401%	$186.522	$186.52	$186.50	$186.50
Purchase #5	$181.81	5.849%	$192.4441	$192.44	$192.45	$192.40
Purchase #6	$69.40	10.462%	$76.6606	$76.66	$76.65	$76.70
Purchase #7	$79.34	13.195%	$89.8089	$89.81	$89.80	$89.80
7 purchase totals =	$1,037.88		$1,129.3698	$1,129.37	$1,129.35	$1,129.40