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	$155.58	7.615%	$167.4274	$167.43	$167.45	$167.40
Purchase #2	$91.33	13.638%	$103.7856	$103.79	$103.80	$103.80
Purchase #3	$154.31	13.816%	$175.6295	$175.63	$175.65	$175.60
Purchase #4	$24.67	3.695%	$25.5816	$25.58	$25.60	$25.60
Purchase #5	$103.55	12.548%	$116.5435	$116.54	$116.55	$116.50
Purchase #6	$85.75	5.785%	$90.7106	$90.71	$90.70	$90.70
Purchase #7	$90.61	3.665%	$93.9309	$93.93	$93.95	$93.90
7 purchase totals =	$705.80		$773.6091	$773.61	$773.70	$773.50