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	$123.61	11.294%	$137.5705	$137.57	$137.55	$137.60
Purchase #2	$60.57	9.198%	$66.1412	$66.14	$66.15	$66.10
Purchase #3	$7.92	11.232%	$8.8096	$8.81	$8.80	$8.80
Purchase #4	$103.71	7.104%	$111.0776	$111.08	$111.10	$111.10
Purchase #5	$90.95	12.410%	$102.2369	$102.24	$102.25	$102.20
Purchase #6	$120.59	11.539%	$134.5049	$134.50	$134.50	$134.50
Purchase #7	$218.60	4.263%	$227.9189	$227.92	$227.90	$227.90
7 purchase totals =	$725.95		$788.2596	$788.26	$788.25	$788.20