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	$235.41	12.394%	$264.5867	$264.59	$264.60	$264.60
Purchase #2	$149.81	12.287%	$168.2172	$168.22	$168.20	$168.20
Purchase #3	$123.63	3.553%	$128.0226	$128.02	$128.00	$128.00
Purchase #4	$134.78	6.435%	$143.4531	$143.45	$143.45	$143.50
Purchase #5	$13.32	10.800%	$14.7586	$14.76	$14.75	$14.80
Purchase #6	$236.91	5.141%	$249.0895	$249.09	$249.10	$249.10
Purchase #7	$61.58	9.461%	$67.4061	$67.41	$67.40	$67.40
7 purchase totals =	$955.44		$1,035.5338	$1,035.54	$1,035.50	$1,035.60