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	$79.52	12.314%	$89.3121	$89.31	$89.30	$89.30
Purchase #2	$155.88	6.834%	$166.5328	$166.53	$166.55	$166.50
Purchase #3	$127.65	4.116%	$132.9041	$132.90	$132.90	$132.90
Purchase #4	$67.77	10.566%	$74.9306	$74.93	$74.95	$74.90
Purchase #5	$95.49	10.546%	$105.5604	$105.56	$105.55	$105.60
Purchase #6	$13.67	12.480%	$15.376	$15.38	$15.40	$15.40
Purchase #7	$234.97	6.625%	$250.5368	$250.54	$250.55	$250.50
7 purchase totals =	$774.95		$835.1528	$835.15	$835.20	$835.10