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	$114.84	7.219%	$123.1303	$123.13	$123.15	$123.10
Purchase #2	$32.96	12.135%	$36.9597	$36.96	$36.95	$37.00
Purchase #3	$67.73	12.596%	$76.2613	$76.26	$76.25	$76.30
Purchase #4	$104.45	6.552%	$111.2936	$111.29	$111.30	$111.30
Purchase #5	$65.55	5.179%	$68.9448	$68.94	$68.95	$68.90
Purchase #6	$52.83	6.760%	$56.4013	$56.40	$56.40	$56.40
Purchase #7	$97.40	8.527%	$105.7053	$105.71	$105.70	$105.70
7 purchase totals =	$535.76		$578.6963	$578.69	$578.70	$578.70