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	$38.39	12.349%	$43.1308	$43.13	$43.15	$43.10
Purchase #2	$118.88	12.299%	$133.5011	$133.50	$133.50	$133.50
Purchase #3	$112.60	3.741%	$116.8124	$116.81	$116.80	$116.80
Purchase #4	$88.87	4.577%	$92.9376	$92.94	$92.95	$92.90
Purchase #5	$73.34	11.860%	$82.0381	$82.04	$82.05	$82.00
Purchase #6	$139.74	8.194%	$151.1903	$151.19	$151.20	$151.20
Purchase #7	$190.78	5.135%	$200.5766	$200.58	$200.60	$200.60
7 purchase totals =	$762.60		$820.1869	$820.19	$820.25	$820.10