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	$9.51	10.698%	$10.5274	$10.53	$10.55	$10.50
Purchase #2	$95.61	13.553%	$108.568	$108.57	$108.55	$108.60
Purchase #3	$84.85	5.326%	$89.3691	$89.37	$89.35	$89.40
Purchase #4	$29.34	8.549%	$31.8483	$31.85	$31.85	$31.80
Purchase #5	$17.88	10.512%	$19.7595	$19.76	$19.75	$19.80
Purchase #6	$150.80	13.735%	$171.5124	$171.51	$171.50	$171.50
Purchase #7	$148.71	4.124%	$154.8428	$154.84	$154.85	$154.80
7 purchase totals =	$536.70		$586.4275	$586.43	$586.40	$586.40