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	$99.25	12.513%	$111.6692	$111.67	$111.65	$111.70
Purchase #2	$21.54	8.371%	$23.3431	$23.34	$23.35	$23.30
Purchase #3	$52.58	12.289%	$59.0416	$59.04	$59.05	$59.00
Purchase #4	$143.92	10.353%	$158.82	$158.82	$158.80	$158.80
Purchase #5	$190.90	12.663%	$215.0737	$215.07	$215.05	$215.10
Purchase #6	$122.44	5.523%	$129.2024	$129.20	$129.20	$129.20
Purchase #7	$94.80	6.322%	$100.7933	$100.79	$100.80	$100.80
7 purchase totals =	$725.43		$797.9433	$797.93	$797.90	$797.90