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	$17.74	4.431%	$18.5261	$18.53	$18.55	$18.50
Purchase #2	$82.72	9.744%	$90.7802	$90.78	$90.80	$90.80
Purchase #3	$55.64	3.406%	$57.5351	$57.54	$57.55	$57.50
Purchase #4	$210.66	12.683%	$237.378	$237.38	$237.40	$237.40
Purchase #5	$83.73	6.246%	$88.9598	$88.96	$88.95	$89.00
Purchase #6	$35.85	10.468%	$39.6028	$39.60	$39.60	$39.60
Purchase #7	$153.76	5.481%	$162.1876	$162.19	$162.20	$162.20
7 purchase totals =	$640.10		$694.9696	$694.98	$695.05	$695.00