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	$59.82	12.847%	$67.5051	$67.51	$67.50	$67.50
Purchase #2	$31.70	3.114%	$32.6871	$32.69	$32.70	$32.70
Purchase #3	$29.88	13.150%	$33.8092	$33.81	$33.80	$33.80
Purchase #4	$214.52	10.775%	$237.6345	$237.63	$237.65	$237.60
Purchase #5	$250.51	9.224%	$273.617	$273.62	$273.60	$273.60
Purchase #6	$206.60	5.795%	$218.5725	$218.57	$218.55	$218.60
Purchase #7	$210.61	6.591%	$224.4913	$224.49	$224.50	$224.50
7 purchase totals =	$1,003.64		$1,088.3167	$1,088.32	$1,088.30	$1,088.30