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	$222.50	10.292%	$245.3997	$245.40	$245.40	$245.40
Purchase #2	$201.28	11.749%	$224.9284	$224.93	$224.95	$224.90
Purchase #3	$30.40	7.638%	$32.722	$32.72	$32.70	$32.70
Purchase #4	$132.94	12.804%	$149.9616	$149.96	$149.95	$150.00
Purchase #5	$118.34	11.120%	$131.4994	$131.50	$131.50	$131.50
Purchase #6	$82.68	10.151%	$91.0728	$91.07	$91.05	$91.10
Purchase #7	$76.40	7.718%	$82.2966	$82.30	$82.30	$82.30
7 purchase totals =	$864.54		$957.8805	$957.88	$957.85	$957.90