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	$247.40	13.473%	$280.7322	$280.73	$280.75	$280.70
Purchase #2	$131.89	7.830%	$142.217	$142.22	$142.20	$142.20
Purchase #3	$13.52	10.205%	$14.8997	$14.90	$14.90	$14.90
Purchase #4	$150.49	5.385%	$158.5939	$158.59	$158.60	$158.60
Purchase #5	$219.73	3.322%	$227.0294	$227.03	$227.05	$227.00
Purchase #6	$66.36	10.821%	$73.5408	$73.54	$73.55	$73.50
Purchase #7	$12.71	6.464%	$13.5316	$13.53	$13.55	$13.50
7 purchase totals =	$842.10		$910.5446	$910.54	$910.60	$910.40