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	$59.82	11.113%	$66.4678	$66.47	$66.45	$66.50
Purchase #2	$250.99	5.370%	$264.4682	$264.47	$264.45	$264.50
Purchase #3	$46.70	9.823%	$51.2873	$51.29	$51.30	$51.30
Purchase #4	$88.29	12.247%	$99.1029	$99.10	$99.10	$99.10
Purchase #5	$77.34	3.354%	$79.934	$79.93	$79.95	$79.90
Purchase #6	$136.70	4.265%	$142.5303	$142.53	$142.55	$142.50
Purchase #7	$137.81	10.148%	$151.795	$151.80	$151.80	$151.80
7 purchase totals =	$797.65		$855.5855	$855.59	$855.60	$855.60