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	$240.38	13.525%	$272.8914	$272.89	$272.90	$272.90
Purchase #2	$227.98	5.458%	$240.4231	$240.42	$240.40	$240.40
Purchase #3	$242.46	13.718%	$275.7207	$275.72	$275.70	$275.70
Purchase #4	$73.58	12.337%	$82.6576	$82.66	$82.65	$82.70
Purchase #5	$149.32	8.602%	$162.1645	$162.16	$162.15	$162.20
Purchase #6	$162.58	11.249%	$180.8686	$180.87	$180.85	$180.90
Purchase #7	$64.36	12.245%	$72.2409	$72.24	$72.25	$72.20
7 purchase totals =	$1,160.66		$1,286.9668	$1,286.96	$1,286.90	$1,287.00