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	$24.89	10.716%	$27.5572	$27.56	$27.55	$27.60
Purchase #2	$221.28	13.614%	$251.4051	$251.41	$251.40	$251.40
Purchase #3	$194.38	11.249%	$216.2458	$216.25	$216.25	$216.20
Purchase #4	$77.40	3.232%	$79.9016	$79.90	$79.90	$79.90
Purchase #5	$94.91	6.291%	$100.8808	$100.88	$100.90	$100.90
Purchase #6	$198.90	5.150%	$209.1434	$209.14	$209.15	$209.10
Purchase #7	$108.58	13.718%	$123.475	$123.48	$123.50	$123.50
7 purchase totals =	$920.34		$1,008.6089	$1,008.62	$1,008.65	$1,008.60