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	$106.73	5.697%	$112.8104	$112.81	$112.80	$112.80
Purchase #2	$59.78	13.572%	$67.8933	$67.89	$67.90	$67.90
Purchase #3	$9.68	11.649%	$10.8076	$10.81	$10.80	$10.80
Purchase #4	$214.73	6.305%	$228.2687	$228.27	$228.25	$228.30
Purchase #5	$35.99	9.179%	$39.2935	$39.29	$39.30	$39.30
Purchase #6	$93.67	12.144%	$105.0453	$105.05	$105.05	$105.00
Purchase #7	$77.88	12.700%	$87.7708	$87.77	$87.75	$87.80
7 purchase totals =	$598.46		$651.8896	$651.89	$651.85	$651.90