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	$135.65	4.669%	$141.9835	$141.98	$142.00	$142.00
Purchase #2	$175.43	9.305%	$191.7538	$191.75	$191.75	$191.80
Purchase #3	$35.88	13.348%	$40.6693	$40.67	$40.65	$40.70
Purchase #4	$173.80	6.606%	$185.2812	$185.28	$185.30	$185.30
Purchase #5	$85.72	6.397%	$91.2035	$91.20	$91.20	$91.20
Purchase #6	$105.59	10.325%	$116.4922	$116.49	$116.50	$116.50
Purchase #7	$46.61	10.227%	$51.3768	$51.38	$51.40	$51.40
7 purchase totals =	$758.68		$818.7603	$818.75	$818.80	$818.90