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	$107.90	12.599%	$121.4943	$121.49	$121.50	$121.50
Purchase #2	$14.89	10.320%	$16.4266	$16.43	$16.45	$16.40
Purchase #3	$29.39	7.329%	$31.544	$31.54	$31.55	$31.50
Purchase #4	$128.42	13.334%	$145.5435	$145.54	$145.55	$145.50
Purchase #5	$223.52	5.144%	$235.0179	$235.02	$235.00	$235.00
Purchase #6	$40.48	13.196%	$45.8217	$45.82	$45.80	$45.80
Purchase #7	$96.52	8.440%	$104.6663	$104.67	$104.65	$104.70
7 purchase totals =	$641.12		$700.5143	$700.51	$700.50	$700.40