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	$156.53	10.249%	$172.5728	$172.57	$172.55	$172.60
Purchase #2	$136.25	10.793%	$150.9555	$150.96	$150.95	$151.00
Purchase #3	$54.83	3.634%	$56.8225	$56.82	$56.80	$56.80
Purchase #4	$150.90	8.840%	$164.2396	$164.24	$164.25	$164.20
Purchase #5	$35.70	8.118%	$38.5981	$38.60	$38.60	$38.60
Purchase #6	$147.46	4.236%	$153.7064	$153.71	$153.70	$153.70
Purchase #7	$78.60	7.514%	$84.506	$84.51	$84.50	$84.50
7 purchase totals =	$760.27		$821.4009	$821.41	$821.35	$821.40