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	$16.89	11.642%	$18.8563	$18.86	$18.85	$18.90
Purchase #2	$228.47	8.768%	$248.5022	$248.50	$248.50	$248.50
Purchase #3	$97.66	5.729%	$103.2549	$103.25	$103.25	$103.30
Purchase #4	$174.94	9.148%	$190.9435	$190.94	$190.95	$190.90
Purchase #5	$49.63	5.522%	$52.3706	$52.37	$52.35	$52.40
Purchase #6	$163.48	9.514%	$179.0335	$179.03	$179.05	$179.00
Purchase #7	$52.78	7.654%	$56.8198	$56.82	$56.80	$56.80
7 purchase totals =	$783.85		$849.7808	$849.77	$849.75	$849.80