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	$16.44	12.415%	$18.481	$18.48	$18.50	$18.50
Purchase #2	$38.57	9.643%	$42.2893	$42.29	$42.30	$42.30
Purchase #3	$78.78	7.668%	$84.8209	$84.82	$84.80	$84.80
Purchase #4	$53.87	5.210%	$56.6766	$56.68	$56.70	$56.70
Purchase #5	$205.89	4.729%	$215.6265	$215.63	$215.65	$215.60
Purchase #6	$59.25	9.126%	$64.6572	$64.66	$64.65	$64.70
Purchase #7	$46.85	6.801%	$50.0363	$50.04	$50.05	$50.00
7 purchase totals =	$499.65		$532.5878	$532.60	$532.65	$532.60