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	$96.67	4.252%	$100.7804	$100.78	$100.80	$100.80
Purchase #2	$76.51	3.348%	$79.0716	$79.07	$79.05	$79.10
Purchase #3	$91.83	9.488%	$100.5428	$100.54	$100.55	$100.50
Purchase #4	$142.30	8.168%	$153.9231	$153.92	$153.90	$153.90
Purchase #5	$19.88	5.529%	$20.9792	$20.98	$21.00	$21.00
Purchase #6	$217.85	6.400%	$231.7924	$231.79	$231.80	$231.80
Purchase #7	$245.85	8.443%	$266.6071	$266.61	$266.60	$266.60
7 purchase totals =	$890.89		$953.6966	$953.69	$953.70	$953.70