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	$60.41	11.373%	$67.2804	$67.28	$67.30	$67.30
Purchase #2	$29.36	10.289%	$32.3809	$32.38	$32.40	$32.40
Purchase #3	$76.34	13.493%	$86.6406	$86.64	$86.65	$86.60
Purchase #4	$229.68	5.120%	$241.4396	$241.44	$241.45	$241.40
Purchase #5	$161.78	11.480%	$180.3523	$180.35	$180.35	$180.40
Purchase #6	$39.82	9.301%	$43.5237	$43.52	$43.50	$43.50
Purchase #7	$161.76	12.868%	$182.5753	$182.58	$182.60	$182.60
7 purchase totals =	$759.15		$834.1928	$834.19	$834.25	$834.20