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	$246.68	10.624%	$272.8873	$272.89	$272.90	$272.90
Purchase #2	$22.38	10.751%	$24.7861	$24.79	$24.80	$24.80
Purchase #3	$25.33	10.117%	$27.8926	$27.89	$27.90	$27.90
Purchase #4	$191.94	13.836%	$218.4968	$218.50	$218.50	$218.50
Purchase #5	$17.44	6.806%	$18.627	$18.63	$18.65	$18.60
Purchase #6	$32.91	13.871%	$37.4749	$37.47	$37.45	$37.50
Purchase #7	$11.77	7.362%	$12.6365	$12.64	$12.65	$12.60
7 purchase totals =	$548.45		$612.8012	$612.81	$612.85	$612.80