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	$12.54	10.254%	$13.8259	$13.83	$13.85	$13.80
Purchase #2	$5.71	9.716%	$6.2648	$6.26	$6.25	$6.30
Purchase #3	$77.28	4.169%	$80.5018	$80.50	$80.50	$80.50
Purchase #4	$127.59	12.124%	$143.059	$143.06	$143.05	$143.10
Purchase #5	$169.76	7.657%	$182.7585	$182.76	$182.75	$182.80
Purchase #6	$235.41	12.200%	$264.13	$264.13	$264.15	$264.10
Purchase #7	$18.33	5.411%	$19.3218	$19.32	$19.30	$19.30
7 purchase totals =	$646.62		$709.8618	$709.86	$709.85	$709.90