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	$65.74	10.107%	$72.3843	$72.38	$72.40	$72.40
Purchase #2	$87.65	7.626%	$94.3342	$94.33	$94.35	$94.30
Purchase #3	$98.68	5.445%	$104.0531	$104.05	$104.05	$104.10
Purchase #4	$141.32	3.519%	$146.2931	$146.29	$146.30	$146.30
Purchase #5	$125.57	3.660%	$130.1659	$130.17	$130.15	$130.20
Purchase #6	$85.60	12.430%	$96.2401	$96.24	$96.25	$96.20
Purchase #7	$23.28	4.206%	$24.2592	$24.26	$24.25	$24.30
7 purchase totals =	$627.84		$667.7299	$667.72	$667.75	$667.80