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	$81.73	9.595%	$89.572	$89.57	$89.55	$89.60
Purchase #2	$140.28	4.507%	$146.6024	$146.60	$146.60	$146.60
Purchase #3	$20.43	4.508%	$21.351	$21.35	$21.35	$21.40
Purchase #4	$96.85	12.223%	$108.688	$108.69	$108.70	$108.70
Purchase #5	$132.28	11.535%	$147.5385	$147.54	$147.55	$147.50
Purchase #6	$159.95	9.599%	$175.3036	$175.30	$175.30	$175.30
Purchase #7	$246.52	11.621%	$275.1681	$275.17	$275.15	$275.20
7 purchase totals =	$878.04		$964.2236	$964.22	$964.20	$964.30