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	$22.62	6.761%	$24.1493	$24.15	$24.15	$24.10
Purchase #2	$56.47	5.863%	$59.7808	$59.78	$59.80	$59.80
Purchase #3	$106.76	5.763%	$112.9126	$112.91	$112.90	$112.90
Purchase #4	$185.89	12.502%	$209.13	$209.13	$209.15	$209.10
Purchase #5	$162.71	8.393%	$176.3663	$176.37	$176.35	$176.40
Purchase #6	$181.81	10.147%	$200.2583	$200.26	$200.25	$200.30
Purchase #7	$71.92	8.534%	$78.0577	$78.06	$78.05	$78.10
7 purchase totals =	$788.18		$860.6550	$860.66	$860.65	$860.70