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	$82.69	3.252%	$85.3791	$85.38	$85.40	$85.40
Purchase #2	$141.86	13.751%	$161.3672	$161.37	$161.35	$161.40
Purchase #3	$136.33	12.771%	$153.7407	$153.74	$153.75	$153.70
Purchase #4	$166.72	3.827%	$173.1004	$173.10	$173.10	$173.10
Purchase #5	$239.92	6.631%	$255.8291	$255.83	$255.85	$255.80
Purchase #6	$130.27	7.353%	$139.8488	$139.85	$139.85	$139.80
Purchase #7	$27.25	9.175%	$29.7502	$29.75	$29.75	$29.80
7 purchase totals =	$925.04		$999.0155	$999.02	$999.05	$999.00