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	$144.52	6.848%	$154.4167	$154.42	$154.40	$154.40
Purchase #2	$218.55	11.582%	$243.8625	$243.86	$243.85	$243.90
Purchase #3	$103.63	8.461%	$112.3981	$112.40	$112.40	$112.40
Purchase #4	$82.81	10.827%	$91.7758	$91.78	$91.80	$91.80
Purchase #5	$184.83	4.175%	$192.5467	$192.55	$192.55	$192.50
Purchase #6	$219.73	6.217%	$233.3906	$233.39	$233.40	$233.40
Purchase #7	$66.53	7.294%	$71.3827	$71.38	$71.40	$71.40
7 purchase totals =	$1,020.60		$1,099.7731	$1,099.78	$1,099.80	$1,099.80