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	$210.92	5.451%	$222.4172	$222.42	$222.40	$222.40
Purchase #2	$85.62	12.865%	$96.635	$96.64	$96.65	$96.60
Purchase #3	$249.59	11.486%	$278.2579	$278.26	$278.25	$278.30
Purchase #4	$18.86	6.276%	$20.0437	$20.04	$20.05	$20.00
Purchase #5	$28.61	4.275%	$29.8331	$29.83	$29.85	$29.80
Purchase #6	$13.76	9.336%	$15.0446	$15.04	$15.05	$15.00
Purchase #7	$63.28	3.570%	$65.5391	$65.54	$65.55	$65.50
7 purchase totals =	$670.64		$727.7706	$727.77	$727.80	$727.60