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	$121.36	8.149%	$131.2496	$131.25	$131.25	$131.20
Purchase #2	$45.43	12.156%	$50.9525	$50.95	$50.95	$51.00
Purchase #3	$200.31	10.571%	$221.4848	$221.48	$221.50	$221.50
Purchase #4	$17.68	12.152%	$19.8285	$19.83	$19.85	$19.80
Purchase #5	$83.91	9.426%	$91.8194	$91.82	$91.80	$91.80
Purchase #6	$155.72	4.429%	$162.6168	$162.62	$162.60	$162.60
Purchase #7	$245.34	10.731%	$271.6674	$271.67	$271.65	$271.70
7 purchase totals =	$869.75		$949.6190	$949.62	$949.60	$949.60