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	$98.59	6.753%	$105.2478	$105.25	$105.25	$105.20
Purchase #2	$79.96	13.258%	$90.5611	$90.56	$90.55	$90.60
Purchase #3	$168.45	9.362%	$184.2203	$184.22	$184.20	$184.20
Purchase #4	$9.87	6.554%	$10.5169	$10.52	$10.50	$10.50
Purchase #5	$140.47	5.795%	$148.6102	$148.61	$148.60	$148.60
Purchase #6	$242.59	8.695%	$263.6832	$263.68	$263.70	$263.70
Purchase #7	$35.33	5.339%	$37.2163	$37.22	$37.20	$37.20
7 purchase totals =	$775.26		$840.0558	$840.06	$840.00	$840.00