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	$35.77	4.226%	$37.2816	$37.28	$37.30	$37.30
Purchase #2	$91.29	10.387%	$100.7723	$100.77	$100.75	$100.80
Purchase #3	$181.97	12.861%	$205.3732	$205.37	$205.35	$205.40
Purchase #4	$213.76	3.233%	$220.6709	$220.67	$220.65	$220.70
Purchase #5	$121.57	5.576%	$128.3487	$128.35	$128.35	$128.30
Purchase #6	$138.52	8.590%	$150.4189	$150.42	$150.40	$150.40
Purchase #7	$126.84	11.144%	$140.975	$140.98	$141.00	$141.00
7 purchase totals =	$909.72		$983.8406	$983.84	$983.80	$983.90