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	$157.97	10.696%	$174.8665	$174.87	$174.85	$174.90
Purchase #2	$34.42	6.314%	$36.5933	$36.59	$36.60	$36.60
Purchase #3	$155.65	12.106%	$174.493	$174.49	$174.50	$174.50
Purchase #4	$62.65	11.369%	$69.7727	$69.77	$69.75	$69.80
Purchase #5	$81.73	9.447%	$89.451	$89.45	$89.45	$89.50
Purchase #6	$40.98	11.666%	$45.7607	$45.76	$45.75	$45.80
Purchase #7	$205.46	9.776%	$225.5458	$225.55	$225.55	$225.50
7 purchase totals =	$738.86		$816.4830	$816.48	$816.45	$816.60