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	$211.80	13.216%	$239.7915	$239.79	$239.80	$239.80
Purchase #2	$51.63	4.650%	$54.0308	$54.03	$54.05	$54.00
Purchase #3	$85.73	5.809%	$90.7101	$90.71	$90.70	$90.70
Purchase #4	$215.56	3.505%	$223.1154	$223.12	$223.10	$223.10
Purchase #5	$101.95	3.472%	$105.4897	$105.49	$105.50	$105.50
Purchase #6	$234.60	10.557%	$259.3667	$259.37	$259.35	$259.40
Purchase #7	$142.77	10.708%	$158.0578	$158.06	$158.05	$158.10
7 purchase totals =	$1,044.04		$1,130.5620	$1,130.57	$1,130.55	$1,130.60