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	$247.54	12.661%	$278.881	$278.88	$278.90	$278.90
Purchase #2	$244.50	5.464%	$257.8595	$257.86	$257.85	$257.90
Purchase #3	$90.69	12.845%	$102.3391	$102.34	$102.35	$102.30
Purchase #4	$100.97	8.265%	$109.3152	$109.32	$109.30	$109.30
Purchase #5	$151.36	12.203%	$169.8305	$169.83	$169.85	$169.80
Purchase #6	$198.53	6.287%	$211.0116	$211.01	$211.00	$211.00
Purchase #7	$18.84	11.754%	$21.0545	$21.05	$21.05	$21.10
7 purchase totals =	$1,052.43		$1,150.2914	$1,150.29	$1,150.30	$1,150.30