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	$102.81	10.376%	$113.4776	$113.48	$113.50	$113.50
Purchase #2	$110.74	5.318%	$116.6292	$116.63	$116.65	$116.60
Purchase #3	$78.35	12.762%	$88.349	$88.35	$88.35	$88.30
Purchase #4	$49.33	4.662%	$51.6298	$51.63	$51.65	$51.60
Purchase #5	$58.77	13.287%	$66.5788	$66.58	$66.60	$66.60
Purchase #6	$104.85	3.747%	$108.7787	$108.78	$108.80	$108.80
Purchase #7	$112.49	13.175%	$127.3106	$127.31	$127.30	$127.30
7 purchase totals =	$617.34		$672.7537	$672.76	$672.85	$672.70