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	$166.48	10.161%	$183.396	$183.40	$183.40	$183.40
Purchase #2	$132.98	8.616%	$144.4376	$144.44	$144.45	$144.40
Purchase #3	$107.82	10.140%	$118.7529	$118.75	$118.75	$118.80
Purchase #4	$149.72	13.255%	$169.5654	$169.57	$169.55	$169.60
Purchase #5	$114.59	3.500%	$118.6007	$118.60	$118.60	$118.60
Purchase #6	$240.95	6.421%	$256.4214	$256.42	$256.40	$256.40
Purchase #7	$101.97	7.430%	$109.5464	$109.55	$109.55	$109.50
7 purchase totals =	$1,014.51		$1,100.7204	$1,100.73	$1,100.70	$1,100.70