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	$216.88	9.874%	$238.2947	$238.29	$238.30	$238.30
Purchase #2	$219.55	9.746%	$240.9473	$240.95	$240.95	$240.90
Purchase #3	$14.54	13.699%	$16.5318	$16.53	$16.55	$16.50
Purchase #4	$79.73	13.545%	$90.5294	$90.53	$90.55	$90.50
Purchase #5	$116.86	9.580%	$128.0552	$128.06	$128.05	$128.10
Purchase #6	$208.38	8.365%	$225.811	$225.81	$225.80	$225.80
Purchase #7	$37.46	7.836%	$40.3954	$40.40	$40.40	$40.40
7 purchase totals =	$893.40		$980.5648	$980.57	$980.60	$980.50