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	$59.45	9.511%	$65.1043	$65.10	$65.10	$65.10
Purchase #2	$231.54	6.410%	$246.3817	$246.38	$246.40	$246.40
Purchase #3	$208.93	7.514%	$224.629	$224.63	$224.65	$224.60
Purchase #4	$59.98	10.126%	$66.0536	$66.05	$66.05	$66.10
Purchase #5	$43.51	4.830%	$45.6115	$45.61	$45.60	$45.60
Purchase #6	$116.43	6.721%	$124.2553	$124.26	$124.25	$124.30
Purchase #7	$99.54	12.192%	$111.6759	$111.68	$111.70	$111.70
7 purchase totals =	$819.38		$883.7113	$883.71	$883.75	$883.80