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	$33.50	11.766%	$37.4416	$37.44	$37.45	$37.40
Purchase #2	$29.91	7.359%	$32.1111	$32.11	$32.10	$32.10
Purchase #3	$241.66	6.682%	$257.8077	$257.81	$257.80	$257.80
Purchase #4	$45.38	9.704%	$49.7837	$49.78	$49.80	$49.80
Purchase #5	$17.62	13.591%	$20.0147	$20.01	$20.00	$20.00
Purchase #6	$75.87	9.175%	$82.8311	$82.83	$82.85	$82.80
Purchase #7	$24.72	13.152%	$27.9712	$27.97	$27.95	$28.00
7 purchase totals =	$468.66		$507.9611	$507.95	$507.95	$507.90