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	$45.55	13.713%	$51.7963	$51.80	$51.80	$51.80
Purchase #2	$78.64	12.636%	$88.577	$88.58	$88.60	$88.60
Purchase #3	$179.91	6.129%	$190.9367	$190.94	$190.95	$190.90
Purchase #4	$38.80	4.627%	$40.5953	$40.60	$40.60	$40.60
Purchase #5	$76.45	7.483%	$82.1708	$82.17	$82.15	$82.20
Purchase #6	$236.27	7.747%	$254.5738	$254.57	$254.55	$254.60
Purchase #7	$56.32	12.642%	$63.44	$63.44	$63.45	$63.40
7 purchase totals =	$711.94		$772.0899	$772.10	$772.10	$772.10