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	$70.28	11.793%	$78.5681	$78.57	$78.55	$78.60
Purchase #2	$113.28	8.184%	$122.5508	$122.55	$122.55	$122.60
Purchase #3	$54.77	8.340%	$59.3378	$59.34	$59.35	$59.30
Purchase #4	$158.95	10.487%	$175.6191	$175.62	$175.60	$175.60
Purchase #5	$206.32	11.234%	$229.498	$229.50	$229.50	$229.50
Purchase #6	$76.81	7.208%	$82.3465	$82.35	$82.35	$82.30
Purchase #7	$32.25	9.833%	$35.4211	$35.42	$35.40	$35.40
7 purchase totals =	$712.66		$783.3414	$783.35	$783.30	$783.30