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	$64.60	11.648%	$72.1246	$72.12	$72.10	$72.10
Purchase #2	$51.55	10.683%	$57.0571	$57.06	$57.05	$57.10
Purchase #3	$64.29	9.650%	$70.494	$70.49	$70.50	$70.50
Purchase #4	$30.48	9.638%	$33.4177	$33.42	$33.40	$33.40
Purchase #5	$195.41	5.123%	$205.4209	$205.42	$205.40	$205.40
Purchase #6	$97.28	5.318%	$102.4534	$102.45	$102.45	$102.50
Purchase #7	$113.79	8.615%	$123.593	$123.59	$123.60	$123.60
7 purchase totals =	$617.40		$664.5607	$664.55	$664.50	$664.60