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	$20.66	6.293%	$21.9601	$21.96	$21.95	$22.00
Purchase #2	$35.58	6.613%	$37.9329	$37.93	$37.95	$37.90
Purchase #3	$81.33	11.866%	$90.9806	$90.98	$91.00	$91.00
Purchase #4	$100.94	13.650%	$114.7183	$114.72	$114.70	$114.70
Purchase #5	$215.87	8.146%	$233.4548	$233.45	$233.45	$233.50
Purchase #6	$139.67	8.706%	$151.8297	$151.83	$151.85	$151.80
Purchase #7	$43.36	13.512%	$49.2188	$49.22	$49.20	$49.20
7 purchase totals =	$637.41		$700.0952	$700.09	$700.10	$700.10