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	$136.76	12.497%	$153.8509	$153.85	$153.85	$153.90
Purchase #2	$120.28	10.858%	$133.34	$133.34	$133.35	$133.30
Purchase #3	$90.42	11.232%	$100.576	$100.58	$100.60	$100.60
Purchase #4	$5.64	6.728%	$6.0195	$6.02	$6.00	$6.00
Purchase #5	$188.56	5.330%	$198.6102	$198.61	$198.60	$198.60
Purchase #6	$18.58	12.588%	$20.9189	$20.92	$20.90	$20.90
Purchase #7	$11.27	5.554%	$11.8959	$11.90	$11.90	$11.90
7 purchase totals =	$571.51		$625.2114	$625.22	$625.20	$625.20