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	$231.85	4.110%	$241.379	$241.38	$241.40	$241.40
Purchase #2	$146.94	10.532%	$162.4157	$162.42	$162.40	$162.40
Purchase #3	$17.37	6.168%	$18.4414	$18.44	$18.45	$18.40
Purchase #4	$153.36	9.142%	$167.3802	$167.38	$167.40	$167.40
Purchase #5	$17.34	7.275%	$18.6015	$18.60	$18.60	$18.60
Purchase #6	$178.40	10.160%	$196.5254	$196.53	$196.55	$196.50
Purchase #7	$134.52	5.590%	$142.0397	$142.04	$142.05	$142.00
7 purchase totals =	$879.78		$946.7829	$946.79	$946.85	$946.70