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	$63.42	13.206%	$71.7952	$71.80	$71.80	$71.80
Purchase #2	$120.81	5.285%	$127.1948	$127.19	$127.20	$127.20
Purchase #3	$112.95	5.141%	$118.7568	$118.76	$118.75	$118.80
Purchase #4	$223.44	13.747%	$254.1563	$254.16	$254.15	$254.20
Purchase #5	$247.38	13.177%	$279.9773	$279.98	$280.00	$280.00
Purchase #6	$210.48	6.233%	$223.5992	$223.60	$223.60	$223.60
Purchase #7	$125.91	6.699%	$134.3447	$134.34	$134.35	$134.30
7 purchase totals =	$1,104.39		$1,209.8243	$1,209.83	$1,209.85	$1,209.90