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	$76.46	11.277%	$85.0824	$85.08	$85.10	$85.10
Purchase #2	$81.55	5.445%	$85.9904	$85.99	$86.00	$86.00
Purchase #3	$29.49	9.803%	$32.3809	$32.38	$32.40	$32.40
Purchase #4	$96.65	9.126%	$105.4703	$105.47	$105.45	$105.50
Purchase #5	$62.89	4.772%	$65.8911	$65.89	$65.90	$65.90
Purchase #6	$79.53	12.225%	$89.2525	$89.25	$89.25	$89.30
Purchase #7	$203.43	8.655%	$221.0369	$221.04	$221.05	$221.00
7 purchase totals =	$630.00		$685.1045	$685.10	$685.15	$685.20