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	$223.93	11.579%	$249.8589	$249.86	$249.85	$249.90
Purchase #2	$90.59	6.305%	$96.3017	$96.30	$96.30	$96.30
Purchase #3	$130.51	9.509%	$142.9202	$142.92	$142.90	$142.90
Purchase #4	$200.81	8.225%	$217.3266	$217.33	$217.35	$217.30
Purchase #5	$174.29	12.276%	$195.6858	$195.69	$195.70	$195.70
Purchase #6	$241.36	3.808%	$250.551	$250.55	$250.55	$250.60
Purchase #7	$90.36	11.280%	$100.5526	$100.55	$100.55	$100.60
7 purchase totals =	$1,151.85		$1,253.1968	$1,253.20	$1,253.20	$1,253.30