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	$23.76	7.481%	$25.5375	$25.54	$25.55	$25.50
Purchase #2	$67.52	6.336%	$71.7981	$71.80	$71.80	$71.80
Purchase #3	$107.89	3.635%	$111.8118	$111.81	$111.80	$111.80
Purchase #4	$74.71	4.308%	$77.9285	$77.93	$77.95	$77.90
Purchase #5	$174.45	10.401%	$192.5945	$192.59	$192.60	$192.60
Purchase #6	$58.69	11.198%	$65.2621	$65.26	$65.25	$65.30
Purchase #7	$93.80	9.678%	$102.878	$102.88	$102.90	$102.90
7 purchase totals =	$600.82		$647.8105	$647.81	$647.85	$647.80