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	$183.59	10.860%	$203.5279	$203.53	$203.55	$203.50
Purchase #2	$105.59	11.481%	$117.7128	$117.71	$117.70	$117.70
Purchase #3	$37.67	4.578%	$39.3945	$39.39	$39.40	$39.40
Purchase #4	$98.49	13.166%	$111.4572	$111.46	$111.45	$111.50
Purchase #5	$49.82	5.520%	$52.5701	$52.57	$52.55	$52.60
Purchase #6	$34.66	10.814%	$38.4081	$38.41	$38.40	$38.40
Purchase #7	$71.93	10.555%	$79.5222	$79.52	$79.50	$79.50
7 purchase totals =	$581.75		$642.5928	$642.59	$642.55	$642.60