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	$136.43	6.123%	$144.7836	$144.78	$144.80	$144.80
Purchase #2	$21.77	10.261%	$24.0038	$24.00	$24.00	$24.00
Purchase #3	$209.98	8.573%	$227.9816	$227.98	$228.00	$228.00
Purchase #4	$79.93	11.129%	$88.8254	$88.83	$88.85	$88.80
Purchase #5	$37.35	9.242%	$40.8019	$40.80	$40.80	$40.80
Purchase #6	$131.56	4.745%	$137.8025	$137.80	$137.80	$137.80
Purchase #7	$151.48	7.146%	$162.3048	$162.30	$162.30	$162.30
7 purchase totals =	$768.50		$826.5036	$826.49	$826.55	$826.50