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	$17.83	13.664%	$20.2663	$20.27	$20.25	$20.30
Purchase #2	$180.36	11.358%	$200.8453	$200.85	$200.85	$200.80
Purchase #3	$151.94	4.248%	$158.3944	$158.39	$158.40	$158.40
Purchase #4	$88.46	3.382%	$91.4517	$91.45	$91.45	$91.50
Purchase #5	$224.88	9.838%	$247.0037	$247.00	$247.00	$247.00
Purchase #6	$124.28	12.104%	$139.3229	$139.32	$139.30	$139.30
Purchase #7	$184.53	8.196%	$199.6541	$199.65	$199.65	$199.70
7 purchase totals =	$972.28		$1,056.9384	$1,056.93	$1,056.90	$1,057.00