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	$154.65	11.503%	$172.4394	$172.44	$172.45	$172.40
Purchase #2	$216.85	7.519%	$233.155	$233.16	$233.15	$233.20
Purchase #3	$211.32	10.209%	$232.8937	$232.89	$232.90	$232.90
Purchase #4	$209.65	11.523%	$233.808	$233.81	$233.80	$233.80
Purchase #5	$227.90	12.152%	$255.5944	$255.59	$255.60	$255.60
Purchase #6	$65.48	4.138%	$68.1896	$68.19	$68.20	$68.20
Purchase #7	$113.46	8.591%	$123.2073	$123.21	$123.20	$123.20
7 purchase totals =	$1,199.31		$1,319.2874	$1,319.29	$1,319.30	$1,319.30