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	$49.47	10.614%	$54.7207	$54.72	$54.70	$54.70
Purchase #2	$244.38	4.384%	$255.0936	$255.09	$255.10	$255.10
Purchase #3	$204.59	11.390%	$227.8928	$227.89	$227.90	$227.90
Purchase #4	$122.72	13.469%	$139.2492	$139.25	$139.25	$139.20
Purchase #5	$21.84	10.127%	$24.0517	$24.05	$24.05	$24.10
Purchase #6	$191.72	6.392%	$203.9747	$203.97	$203.95	$204.00
Purchase #7	$54.27	4.810%	$56.8804	$56.88	$56.90	$56.90
7 purchase totals =	$888.99		$961.8631	$961.85	$961.85	$961.90