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	$14.25	5.239%	$14.9966	$15.00	$15.00	$15.00
Purchase #2	$102.90	7.545%	$110.6638	$110.66	$110.65	$110.70
Purchase #3	$29.73	13.476%	$33.7364	$33.74	$33.75	$33.70
Purchase #4	$204.67	7.261%	$219.5311	$219.53	$219.55	$219.50
Purchase #5	$55.61	6.325%	$59.1273	$59.13	$59.15	$59.10
Purchase #6	$40.59	4.471%	$42.4048	$42.40	$42.40	$42.40
Purchase #7	$206.96	11.866%	$231.5179	$231.52	$231.50	$231.50
7 purchase totals =	$654.71		$711.9779	$711.98	$712.00	$711.90