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	$203.78	12.143%	$228.525	$228.53	$228.55	$228.50
Purchase #2	$168.53	11.688%	$188.2278	$188.23	$188.25	$188.20
Purchase #3	$99.97	11.464%	$111.4306	$111.43	$111.45	$111.40
Purchase #4	$116.28	10.405%	$128.3789	$128.38	$128.40	$128.40
Purchase #5	$145.32	10.706%	$160.878	$160.88	$160.90	$160.90
Purchase #6	$52.70	7.205%	$56.497	$56.50	$56.50	$56.50
Purchase #7	$55.46	13.261%	$62.8146	$62.81	$62.80	$62.80
7 purchase totals =	$842.04		$936.7519	$936.76	$936.85	$936.70